Imaging device and camera system, and driving method of imaging device

ABSTRACT

An imaging device includes: a photoelectric converter including first and second electrodes, and a photoelectric conversion layer located between the first electrode and the second electrode; a voltage supply circuit applying a bias voltage between the first electrode and the second electrode; an amplifier transistor including a gate electrically connected to the second electrode, the amplifier transistor configured to output a signal corresponding to a potential of the second electrode; and a detection circuit configured to detect a level of the signal from the amplifier transistor. The voltage supply circuit applies the bias voltage in a first voltage range when the level detected by the detection circuit is greater than or equal to a first threshold value, and applies the bias voltage in a second voltage range that is greater than the first voltage range when the level detected by the detection circuit is less than a second threshold value.

CROSS-REFERENCE OF RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.16/907,742, filed on Jun. 22, 2020, which is a Continuation of U.S.patent application Ser. No. 16/257,607, filed on Jan. 25, 2019, now U.S.Pat. No. 10,734,421, which claims the benefit of Japanese ApplicationNo. 2018-021278, filed on Feb. 8, 2018, the entire disclosures of whichapplications are incorporated by reference herein.

BACKGROUND 1. Technical Field

The present disclosure relates to an imaging device and a camera system.The present disclosure also relates to a driving method of an imagingdevice.

2. Description of the Related Art

In the field of imaging devices, a configuration is known in which,instead of a photodiode, a photoelectric conversion layer is arrangedabove a semiconductor substrate on which a read circuit is formed. Thiskind of configuration is referred to as a stacked type. For example,Japanese Unexamined Patent Application Publication No. 2011-228648discloses an imaging element that has an organic photoelectricconversion layer sandwiched between a pixel electrode and a transparentopposite electrode, above a substrate on which a read circuit is formed.During operation, a predetermined voltage is applied to the oppositeelectrode.

The specification of U.S. Pat. No. 9,054,246 discloses an imaging systemhaving a quantum dot layer that serves as a photoelectric conversionlayer. Furthermore, the specification of U.S. Pat. No. 9,054,246discloses that the gain of the quantum dot layer is adjusted by alteringa potential difference applied between a transparent electrode and apixel electrode arranged on either side of the quantum dot layer.

SUMMARY

It is beneficial if power consumption can be further reduced.

A non-limiting exemplary embodiment of the present disclosure providesthe following, for example.

In one general aspect, the techniques disclosed here feature an imagingdevice including: a photoelectric converter that includes a firstelectrode, a second electrode, and a photoelectric conversion layerlocated between the first electrode and the second electrode; a voltagesupply circuit that applies a bias voltage between the first electrodeand the second electrode; an amplifier transistor that includes a gateelectrically connected to the second electrode, the amplifier transistorbeing configured to output a signal that corresponds to a potential ofthe second electrode; and a detection circuit that is configured todetect a level of the signal from the amplifier transistor. The voltagesupply circuit applies the bias voltage in a first voltage range, in acase where the level detected by the detection circuit is greater thanor equal to a first threshold value, and applies the bias voltage in asecond voltage range that is greater than the first voltage range, in acase where the level detected by the detection circuit is less than asecond threshold value.

General or specific aspects may be realized by means of an element, adevice, a system, an integrated circuit, a method, or a computerprogram. Furthermore, general or specific aspects may be realized bymeans of an arbitrary combination of an element, a device, an apparatus,a system, an integrated circuit, a method, and a computer program.

Additional benefits and advantages of the disclosed embodiments will beapparent from the specification and the drawings. The benefits and/oradvantages may be individually provided by the various embodiments orfeatures disclosed in the specification and the drawings, and need notall be provided in order to obtain one or more of the same.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing schematically depicting an exemplary configurationof an imaging device according to a first embodiment of the presentdisclosure;

FIG. 2 is a drawing depicting an exemplary circuit configuration of theimaging device depicted in FIG. 1 ;

FIG. 3A is a cross-sectional view schematically depicting an exemplarydevice structure of a pixel;

FIG. 3B is a schematic cross-sectional view for describing an operationof the pixel in a case where electrons are used as signal charges;

FIG. 4 is a drawing depicting a typical example of the photoelectricconversion characteristics of a photoelectric conversion layer;

FIG. 5 is a drawing for describing an example of a method of determiningspecific ranges for a first voltage range and a second voltage range;

FIG. 6 is a drawing for describing another example of a method ofdetermining specific ranges for the first voltage range and the secondvoltage range;

FIG. 7 is a drawing for describing yet another example of a method ofdetermining specific ranges for the first voltage range and the secondvoltage range;

FIG. 8 is a schematic flowchart depicting a first exemplary operation ofthe imaging device;

FIG. 9 is a schematic cross-sectional view for describing a change inphotoelectric conversion efficiency with respect to a change inilluminance, when a voltage of 2 V is applied as a first voltage to anopposite electrode;

FIG. 10 is a schematic cross-sectional view for describing a change inphotoelectric conversion efficiency with respect to a change inilluminance, when a voltage of 2 V is applied as the first voltage tothe opposite electrode, and schematically depicts a state in whichelectron holes are accumulated in an impurity region;

FIG. 11 is a drawing schematically depicting a typical example of achange in the level of a signal from an output circuit, with respect toa change in the quantity of light incident on a photoelectric conversionunit;

FIG. 12 is a drawing schematically depicting a state in which apotential difference is increased by applying a second voltage to avoltage line from a voltage supply circuit;

FIG. 13 is a drawing schematically depicting a typical example of achange in the level of the signal from the output circuit, with respectto a change in the quantity of light incident on the photoelectricconversion unit, when the second voltage is applied to the oppositeelectrode;

FIG. 14 is a schematic cross-sectional view depicting a configuration inwhich a third electrode is arranged between two pixel electrodes thatare adjacent to each other;

FIG. 15 is a schematic plan view depicting an example of the arrangementrelationship between a pixel electrode and the third electrode, whenseen from the opposite electrode side;

FIG. 16 is a schematic cross-sectional view for describing a mechanismthat further lowers the effective photoelectric conversion efficiency byapplying a predetermined voltage to the third electrode;

FIG. 17 is a drawing schematically depicting another typical example ofa change in the level of the signal from the output circuit, withrespect to a change in the quantity of light incident on thephotoelectric conversion unit, when the first voltage is applied to theopposite electrode, and when the second voltage is applied to theopposite electrode;

FIG. 18 is a schematic cross-sectional view for describing an operationof the pixels at a high illuminance in a second operation example, andis a drawing depicting a state in which a voltage of 6 V, which is anintermediate magnitude, is applied as the first voltage to the oppositeelectrode;

FIG. 19 is a schematic cross-sectional view for describing an operationof the pixels at a low illuminance in the second operation example, andis a drawing depicting a state in which a voltage of 12 V is applied asthe second voltage to the opposite electrode;

FIG. 20A is a drawing depicting an exemplary circuit configuration of animaging device according to a modified example of the first embodiment;

FIG. 20B is a drawing depicting an exemplary circuit configuration of animaging device according to another modified example of the firstembodiment;

FIG. 21A is a drawing schematically depicting an exemplary configurationof a camera system according to a second embodiment of the presentdisclosure;

FIG. 21B is a drawing schematically depicting another exemplaryconfiguration of the camera system according to the second embodiment ofthe present disclosure;

FIG. 22 is a drawing schematically depicting yet another exemplaryconfiguration of the camera system according to the second embodiment ofthe present disclosure;

FIG. 23 is a drawing depicting a modified example of a light quantitydetector;

FIG. 24 is a drawing schematically depicting yet another exemplaryconfiguration of the camera system according to the second embodiment ofthe present disclosure;

FIG. 25 is a drawing for describing the relationship between the timingof switching between the first voltage and the second voltage, and achange in the level of a signal acquired by a detection circuit, whichaccompanies the switching of the voltage;

FIG. 26 is a drawing depicting another example of the timing ofswitching between the first voltage and the second voltage;

FIG. 27 is a drawing depicting yet another example of the timing ofswitching between the first voltage and the second voltage;

FIG. 28 is a drawing for describing the relationship between the timingof switching between the first voltage and the second voltage when aglobal shutter implemented by controlling a potential difference isapplied, and a change in the level of the signal acquired by thedetection circuit, which accompanies the switching of the voltage;

FIG. 29 is a drawing for describing an example of the relationshipbetween the timing of switching between the first voltage and the secondvoltage, and an output from the imaging device;

FIG. 30 is a drawing depicting an application example of mask processingin a case where switching between the first voltage and the secondvoltage has been executed during a row scanning period for readingsignals;

FIG. 31 is a drawing for describing an example of a processing sequencein an automatic exposure setting process, which can be applied in animaging device and a camera system according to embodiments of thepresent disclosure;

FIG. 32 is a schematic plan view for describing an example in which aregion including the photoelectric conversion units of some or all ofthe pixels included in an imaging region is used as an exposure quantitydetection region;

FIG. 33 is a diagram depicting an example of processing in which avoltage that is output from the voltage supply circuit is alteredaccording to the exposure quantity detected;

FIG. 34 is a diagram depicting another example of processing in whichthe voltage that is output from the voltage supply circuit is alteredaccording to the exposure quantity detected;

FIG. 35 is a diagram depicting yet another example of processing inwhich the voltage that is output from the voltage supply circuit isaltered according to the exposure quantity detected;

FIG. 36 is a drawing schematically depicting an example of a change inthe output of the detection circuit, with respect to an increase in theexposure quantity;

FIG. 37 is a block diagram schematically depicting an overview oflinearity compensation processing;

FIG. 38 is a drawing depicting an example of a correction table;

FIG. 39 is a drawing for describing differences in deviation inlinearity according to the imaging device or according to the camerasystem;

FIG. 40 is a block diagram schematically depicting an overview oflinearity compensation processing in which differences according to theimaging device or according to the camera system are canceled;

FIG. 41 is a drawing depicting an example of a correction table storedin a memory of an imaging device of sample 1;

FIG. 42 is a drawing depicting an example of a correction table storedin the memory of an imaging device of sample 2;

FIG. 43 is a drawing depicting another example of a correction tablestored in the memory;

FIG. 44 is a drawing depicting the plotting of output values given inthe correction table of FIG. 43 ; and

FIG. 45 is a drawing schematically depicting an overview of linearitycompensation processing including interpolation processing.

DETAILED DESCRIPTION

As described in Japanese Unexamined Patent Application Publication No.2011-228648, a comparatively high voltage that exceeds a power sourcevoltage may be required for a voltage that is to be applied to anopposite electrode in a stacked configuration. It is beneficial if powerconsumption can be further reduced.

An overview of an aspect of the present disclosure is as follows.

[Item 1]

An imaging device provided with:

a photoelectric converter that includes a first electrode, a secondelectrode, and a photoelectric conversion layer located between thefirst electrode and the second electrode;

a voltage supply circuit;

an output circuit that is coupled to the second electrode, the outputcircuit being configured to output a signal that corresponds to apotential of the second electrode; and

a detection circuit that is configured to detect a level of the signalfrom the output circuit, wherein

the photoelectric converter has photoelectric conversion characteristicsin which a first rate of change is greater than a second rate of change,the first rate of change being a rate of change of a photoelectricconversion efficiency of the photoelectric converter with respect to abias voltage applied between the first electrode and the secondelectrode when the bias voltage is in a first voltage range, the secondrate of change being a rate of change of the photoelectric conversionefficiency of the photoelectric converter with respect to the biasvoltage when the bias voltage is in a second voltage range that ishigher than the first voltage range, and

the voltage supply circuit

-   -   applies a voltage to one of the first electrode and the second        electrode to cause a potential difference between the first        electrode and the second electrode to be a first potential        difference, in a case where the level detected by the detection        circuit is greater than or equal to a first threshold value, and    -   applies a voltage to the one of the first electrode and the        second electrode to cause the potential difference between the        first electrode and the second electrode to be a second        potential difference that is greater than the first potential        difference, in a case where the level detected by the detection        circuit is less than a second threshold value that is less than        or equal to the first threshold value.        [Item 2]

The imaging device according to item 1, wherein

the voltage supply circuit,

-   -   applies a first voltage to the one of the first electrode and        the second electrode, in a case where the level detected by the        detection circuit is greater than or equal to the first        threshold value, and    -   applies a second voltage that is higher than the first voltage        to the one of the first electrode and the second electrode, in a        case where the level detected by the detection circuit is lower        than the second threshold value.        [Item 3]

The imaging device according to item 2, wherein a potential of the firstelectrode is higher than the potential of the second electrode in bothof a state in which the first voltage is applied to the one of the firstelectrode and the second electrode, and a state in which the secondvoltage is applied to the one of the first electrode and the secondelectrode.

[Item 4]

The imaging device according to item 2 or 3, wherein, in a graph of thephotoelectric conversion efficiency of the photoelectric converter withrespect to the bias voltage, when Vt is a value of the bias voltagecorresponding to an intersecting point between a first tangent at apoint where the photoelectric conversion efficiency rises from 0 and asecond tangent at a point where the bias voltage is a largest valueduring operation, the first voltage range is a voltage range that isless than the Vt.

[Item 5]

The imaging device according to item 2 or 3, wherein, in a graph of thephotoelectric conversion efficiency of the photoelectric converter withrespect to the bias voltage, when Vt is a value of the bias voltagecorresponding to an intersecting point between a first tangent at apoint where a value of the photoelectric conversion efficiency is 0.06and a second tangent at a point where the bias voltage is a largestvalue during operation, the first voltage range is a voltage range thatis less than the Vt.

[Item 6]

The imaging device according to item 2 or 3, wherein the second voltagerange is a voltage range in which a change in the photoelectricconversion efficiency with respect to a change of 1 V in the biasvoltage is less than 10%.

[Item 7]

The imaging device according to item 2 or 3, wherein the second voltagerange is a voltage range in which the photoelectric conversionefficiency is 0.7 or more.

[Item 8]

The imaging device according to any one of items 4 to 7, wherein a firstefficiency that is the photoelectric conversion efficiency of thephotoelectric converter when the first voltage is supplied is lower thana second efficiency that is the photoelectric conversion efficiency ofthe photoelectric converter when the second voltage is supplied.

[Item 9]

The imaging device according to item 8, wherein

the first voltage is within the first voltage range, and

the second voltage is within the second voltage range.

[Item 10]

The imaging device according to item 9, wherein a ratio of the secondvoltage with respect to the first voltage is greater than a ratio of thesecond efficiency with respect to the first efficiency.

[Item 11]

The imaging device according to item 10, wherein the ratio of the secondefficiency with respect to the first efficiency is 1.25 or more and 100or less.

[Item 12]

The imaging device according to item 8, wherein the first voltage andthe second voltage are within the second voltage range.

[Item 13]

The imaging device according to item 12, wherein a ratio of the secondefficiency with respect to the first efficiency is 1 or more and 1.25 orless.

[Item 14]

A camera system provided with:

an imaging device including:

-   -   a photoelectric converter that includes a first electrode, a        second electrode, and a photoelectric conversion layer located        between the first electrode and the second electrode,    -   a voltage supply circuit, and    -   an output circuit that is coupled to the second electrode, the        output circuit being configured to output a signal that        corresponds to a potential of the second electrode; and

a light quantity detector that detects a quantity of light incident onthe photoelectric converter, wherein

the photoelectric converter has photoelectric conversion characteristicsin which a first rate of change is greater than a second rate of change,the first rate of change being a rate of change of a photoelectricconversion efficiency of the photoelectric converter with respect to abias voltage applied between the first electrode and the secondelectrode when the bias voltage is in a first voltage range, the secondrate being a rate of change of the photoelectric conversion efficiencyof the photoelectric converter with respect to the bias voltage when thebias voltage is in a second voltage range that is higher than the firstvoltage range, and

the voltage supply circuit

-   -   applies a voltage to one of the first electrode and the second        electrode to cause a potential difference between the first        electrode and the second electrode to be a first potential        difference, in a case where the quantity of light detected by        the light quantity detector is greater than or equal to a first        quantity of light, and,    -   applies a voltage to the one of the first electrode and the        second electrode to cause the potential difference between the        first electrode and the second electrode to be a second        potential difference that is greater than the first potential        difference, in a case where the quantity of light detected by        the light quantity detector is less than a second quantity of        light that is less than or equal to the first quantity of light.        [Item 15]

A driving method of an imaging device that has a photoelectric converterthat includes a first electrode, a second electrode, and a photoelectricconversion layer located between the first electrode and the secondelectrode, the driving method comprising:

supplying a voltage to one of the first electrode and the secondelectrode to cause a potential difference between the first electrodeand the second electrode to be a first potential difference, in a casewhere a quantity of light incident on the photoelectric converter isgreater than or equal to a first quantity of light, and

supplying a voltage to the one of the first electrode and the secondelectrode to cause the potential difference between the first electrodeand the second electrode to be a second potential difference that isgreater than the first potential difference, in a case where thequantity of light incident on the photoelectric converter is less than asecond quantity of light that is less than or equal to the firstquantity of light.

[Item 16]

An imaging device provided with:

a photoelectric conversion unit that includes a first electrode, asecond electrode, and a photoelectric conversion layer located betweenthe first electrode and the second electrode;

a voltage supply circuit that is coupled to one of the first electrodeand the second electrode;

an output circuit that is coupled to the second electrode, and outputs asignal that corresponds to a potential of the second electrode; and

a detection circuit that detects a level of the signal from the outputcircuit,

in which a rate of change of a photoelectric conversion efficiency ofthe photoelectric conversion unit with respect to a bias voltage, whichis applied between the first electrode and the second electrode, whenthe bias voltage is in a first voltage range is greater than when thebias voltage is in a second voltage range that is higher than the firstvoltage range, and

the voltage supply circuit,

in a case where the level detected by the detection circuit is greaterthan or equal to a predetermined threshold value, applies a voltage tothe one of the first electrode and the second electrode in such a waythat a potential difference between the first electrode and the secondelectrode becomes a first potential difference, and,

in a case where the level detected by the detection circuit is lowerthan the threshold value, applies a voltage to the one of the firstelectrode and the second electrode in such a way that the potentialdifference between the first electrode and the second electrode becomesa second potential difference that is greater than the first potentialdifference.

According to the configuration of item 16, in a situation where theilluminance is high, the bias voltage that is applied between the firstelectrode and the second electrode decreases, and therefore thesensitivity of the photoelectric conversion unit decreases. In otherwords, an ND filter function implemented by means of electrical controlis realized. Furthermore, at such time, the effect of a reduction inpower consumption can be expected.

[Item 17]

The imaging device according to item 16,

in which the voltage supply circuit, in a case where the level detectedby the detection circuit is greater than or equal to the thresholdvalue, applies a first voltage to the one of the first electrode and thesecond electrode, and, in a case where the level detected by thedetection circuit is lower than the threshold value, applies a secondvoltage that is higher than the first voltage to the one of the firstelectrode and the second electrode.

According to the configuration of item 17, in a situation where theilluminance is high, from among the mutually different voltages, therelatively low first voltage is selectively applied to the photoelectricconversion unit from the voltage supply circuit. Therefore, it becomespossible for power consumption to be reduced compared to a configurationin which a comparatively high voltage of approximately 10 V is appliedto the photoelectric conversion unit regardless of the illuminance.

[Item 18]

The imaging device according to item 17, in which a potential of thefirst electrode is higher than the potential of the second electrode inboth of a state in which the first voltage is applied to the one of thefirst electrode and the second electrode and a state in which the secondvoltage is applied to the one of the first electrode and the secondelectrode.

According to the configuration of item 18, positive charges from amongthe charges generated by photoelectric conversion can be collected bythe second electrode, and electron holes can be accumulated in a chargeaccumulation region as signal charges. Furthermore, the potential of thecharge accumulation region gradually rises due to continued accumulationof the signal charges, and therefore the effective bias voltageaccording to the photoelectric conversion layer can be made to be lessthan the value of the second voltage.

[Item 19]

The imaging device according to item 17 or 18,

in which, in a graph of the photoelectric conversion efficiency of thephotoelectric conversion unit with respect to the bias voltage, when Vtis a value of the bias voltage corresponding to an intersecting pointbetween a first tangent at a point where the photoelectric conversionefficiency rises from 0 and a second tangent at a point where the biasvoltage is the largest value during operation, the first voltage rangeis a voltage range that is less than Vt.

[Item 20]

The imaging device according to item 17 or 18,

in which, in a graph of the photoelectric conversion efficiency of thephotoelectric conversion unit with respect to the bias voltage, when Vtis a value of the bias voltage corresponding to an intersecting pointbetween a first tangent at a point where the value of the photoelectricconversion efficiency becomes 0.06 and a second tangent at a point wherethe bias voltage is the largest value during operation, the firstvoltage range is a voltage range that is less than Vt.

[Item 21]

The imaging device according to item 17 or 18,

in which the second voltage range is a voltage range in which a changein the photoelectric conversion efficiency with respect to a change of 1V in the bias voltage is less than 10%.

[Item 22]

The imaging device according to item 17 or 18,

in which the second voltage range is a voltage range in which thephotoelectric conversion efficiency is 0.7 or more.

According to the configuration of item 22, it is easy to achievecorrespondence between the magnitude of the bias voltage applied betweenthe first electrode and the second electrode and ISO numerical values.

[Item 23]

The imaging device according to any one of items 19 to 22, in which afirst efficiency that is the photoelectric conversion efficiency of thephotoelectric conversion unit when the first voltage is being suppliedis lower than a second efficiency that is the photoelectric conversionefficiency of the photoelectric conversion unit when the second voltageis being supplied.

According to the configuration of item 23, by applying the relativelylow first voltage to the photoelectric conversion unit to reduce thepotential difference between the first electrode and the secondelectrode, the sensitivity of pixels can be decreased.

[Item 24]

The imaging device according to item 23,

in which the first voltage is a voltage within the first voltage range,and

the second voltage is a voltage within the second voltage range.

According to the configuration of item 24, it is possible for the levelof the signal to automatically decrease in accordance with an increasein the quantity of light, and it is therefore possible to obtain theeffect of an expansion in the dynamic range relating to the direction inwhich the illuminance is high.

[Item 25]

The imaging device according to item 24,

in which a ratio of the second voltage with respect to the first voltageis greater than a ratio of the second efficiency with respect to thefirst efficiency.

[Item 26]

The imaging device according to item 25,

in which the ratio of the second efficiency with respect to the firstefficiency is 1.25 or more.

[Item 27]

The imaging device according to item 23,

in which the first voltage and the second voltage are voltages withinthe second voltage range.

According to the configuration of item 27, an advantage can be obtainedin that reliability is easily ensured since high-voltage elements arenot required, and power saving and high-speed driving can be expectedwhen the first voltage is being supplied.

[Item 28]

The imaging device according to item 27,

in which the ratio of the second efficiency with respect to the firstefficiency is 1 or more and 1.25 or less.

[Item 29]

The imaging device according to any one of items 16 to 28,

further provided with a charge accumulation unit that is coupled to thesecond electrode, and temporarily accumulates charges collected by thesecond electrode, in which a potential of the charge accumulation unitincreases together with accumulation of charges in the chargeaccumulation unit.

According to the configuration of item 29, the effective bias voltageaccording to the photoelectric conversion layer changes according to theilluminance. Consequently, in a state in which the voltage supplycircuit is outputting the first voltage of the first voltage range, theeffect of an expansion in the dynamic range can be obtained.Furthermore, in a case where the first voltage and the second voltageare selected from the second voltage range, high-voltage elements andelement isolation regions are not required, and therefore highreliability is easily ensured.

[Item 30]

The imaging device according to any one of items 16 to 29,

including a plurality of pixels each having a photoelectric conversionunit and an output circuit, the plurality of pixels including a firstpixel and a second pixel that is arranged adjacent to the first pixel,and

further provided with a third electrode that is located between thesecond electrode of the first pixel and the second electrode of thesecond pixel, and is electrically insulated from the second electrode ofthe first pixel and the second electrode of the second pixel.

According to the configuration of item 30, by adjusting the potential ofthe third electrode, it is possible for charges generated in thevicinity of the boundary between the two pixels to be preferentiallycollected by the third electrode. As a result, it becomes possible forthe effective photoelectric conversion efficiency to be furtherdecreased, and the dynamic range relating to the direction in which theilluminance is high to be further expanded.

[Item 31]

A camera system provided with:

an imaging device that has a photoelectric conversion unit that includesa first electrode, a second electrode, and a photoelectric conversionlayer located between the first electrode and the second electrode; and

a voltage supply circuit that is coupled to one of the first electrodeand the second electrode,

in which the imaging device further has:

an output circuit that is coupled to the second electrode, and outputs asignal that corresponds to a potential of the second electrode; and

a detection circuit that detects a level of the signal from the outputcircuit,

a rate of change of a photoelectric conversion efficiency of thephotoelectric conversion unit with respect to a bias voltage, which isapplied between the first electrode and the second electrode, when thebias voltage is in a first voltage range is greater than when the biasvoltage is in a second voltage range that is higher than the firstvoltage range, and

the voltage supply circuit,

in a case where the level detected by the detection circuit is greaterthan or equal to a predetermined threshold value, applies a voltage tothe one of the first electrode and the second electrode in such a waythat a potential difference between the first electrode and the secondelectrode becomes a first potential difference, and,

in a case where the level detected by the detection circuit is lowerthan the threshold value, applies a voltage to the one of the firstelectrode and the second electrode in such a way that the potentialdifference between the first electrode and the second electrode becomesa second potential difference that is greater than the first potentialdifference.

According to the configuration of item 31, an effect that is similar tothat of item 16 can be obtained.

[Item 32]

The camera system according to item 31,

in which the voltage supply circuit,

in a case where the level detected by the detection circuit is greaterthan or equal to the threshold value, applies a first voltage to the oneof the first electrode and the second electrode, and,

in a case where the level detected by the detection circuit is lowerthan the threshold value, applies a second voltage that is higher thanthe first voltage to the one of the first electrode and the secondelectrode.

According to the configuration of item 32, an effect that is similar tothat of item 17 can be obtained.

[Item 33]

A camera system provided with:

an imaging device that has a photoelectric conversion unit that includesa first electrode, a second electrode, and a photoelectric conversionlayer located between the first electrode and the second electrode; and

a light quantity detector that detects a quantity of light incident onthe photoelectric conversion unit,

in which the imaging device further has:

an output circuit that is coupled to the second electrode, and outputs asignal that corresponds to a potential of the second electrode; and

a voltage supply circuit that is coupled to one of the first electrodeand the second electrode,

a rate of change of a photoelectric conversion efficiency of thephotoelectric conversion unit with respect to a bias voltage, which isapplied between the first electrode and the second electrode, when thebias voltage is in a first voltage range is greater than when the biasvoltage is in a second voltage range that is higher than the firstvoltage range, and

the voltage supply circuit,

in a case where the quantity of light detected by the light quantitydetector is greater than or equal to a predetermined quantity of light,applies a voltage to the one of the first electrode and the secondelectrode in such a way that a potential difference between the firstelectrode and the second electrode becomes a first potential difference,and,

in a case where the quantity of light detected by the light quantitydetector is less than the predetermined quantity of light, applies avoltage to the one of the first electrode and the second electrode insuch a way that the potential difference between the first electrode andthe second electrode becomes a second potential difference that isgreater than the first potential difference.

According to the configuration of item 33, an effect that is similar tothat of item 16 can be obtained.

[Item 34]

A camera system provided with:

an imaging device that has a photoelectric conversion unit that includesa first electrode, a second electrode, and a photoelectric conversionlayer located between the first electrode and the second electrode;

a voltage supply circuit that is coupled to one of the first electrodeand the second electrode; and

a light quantity detector that detects a quantity of light incident onthe photoelectric conversion unit,

in which a rate of change of a photoelectric conversion efficiency ofthe photoelectric conversion unit with respect to a bias voltage, whichis applied between the first electrode and the second electrode, whenthe bias voltage is in a first voltage range is greater than when thebias voltage is in a second voltage range that is higher than the firstvoltage range,

the imaging device further has an output circuit that is coupled to thesecond electrode, and outputs a signal that corresponds to a potentialof the second electrode, and

the voltage supply circuit,

in a case where the quantity of light detected by the light quantitydetector is greater than or equal to a predetermined quantity of light,applies a voltage to the one of the first electrode and the secondelectrode in such a way that a potential difference between the firstelectrode and the second electrode becomes a first potential difference,and,

in a case where the quantity of light detected by the light quantitydetector is less than the predetermined quantity of light, applies avoltage to the one of the first electrode and the second electrode insuch a way that the potential difference between the first electrode andthe second electrode becomes a second potential difference that isgreater than the first potential difference.

According to the configuration of item 34, an effect that is similar tothat of item 16 can be obtained.

[Item 35]

The camera system according to item 33 or 34,

in which the light quantity detector includes a light quantity detectioncircuit that detects the level of the signal from the output circuit.

According to the configuration of item 35, information relating to thequantity of light incident on the photoelectric conversion unit can beobtained by way of detecting the level of the signal that is output froma pixel.

[Item 36]

The camera system according to any one of items 33 to 35,

in which the voltage supply circuit,

in a case where the quantity of light detected by the light quantitydetector is greater than or equal to the predetermined quantity oflight, applies a first voltage to the one of the first electrode and thesecond electrode, and,

in a case where the quantity of light detected by the light quantitydetector is less than the predetermined quantity of light, applies asecond voltage that is higher than the first voltage to the one of thefirst electrode and the second electrode.

According to the configuration of item 36, an effect that is similar tothat of item 17 can be obtained.

[Item 37]

The camera system according to item 32 or 36,

in which a potential of the first electrode is higher than the potentialof the second electrode in both of a state in which the first voltage isapplied to the one of the first electrode and the second electrode and astate in which the second voltage is applied to the one of the firstelectrode and the second electrode.

According to the configuration of item 37, an effect that is similar tothat of item 18 can be obtained.

[Item 38]

The camera system according to item 32, 36, or 37,

in which, in a graph of the photoelectric conversion efficiency of thephotoelectric conversion unit with respect to the bias voltage, when Vtis a value of the bias voltage corresponding to an intersecting pointbetween a first tangent at a point where the photoelectric conversionefficiency rises from 0 and a second tangent at a point where the biasvoltage is the largest value during operation, the first voltage rangeis a voltage range that is less than Vt.

[Item 39]

The camera system according to item 32, 36, or 37,

in which, in a graph of the photoelectric conversion efficiency of thephotoelectric conversion unit with respect to the bias voltage, when Vtis a value of the bias voltage corresponding to an intersecting pointbetween a first tangent at a point where a value of the photoelectricconversion efficiency becomes 0.06 and a second tangent at a point wherethe bias voltage is the largest value during operation, the firstvoltage range is a voltage range that is less than Vt.

[Item 40]

The camera system according to item 32, 36, or 37,

in which the second voltage range is a voltage range in which a changein the photoelectric conversion efficiency with respect to a change of 1V in the bias voltage is less than 10%.

[Item 41]

The camera system according to item 32, 36, or 37,

in which the second voltage range is a voltage range in which thephotoelectric conversion efficiency is 0.7 or more.

According to the configuration of item 41, an effect that is similar tothat of item 22 can be obtained.

[Item 42]

The camera system according to any one of items 38 to 41,

in which a first efficiency that is the photoelectric conversionefficiency of the photoelectric conversion unit when the first voltageis being supplied is lower than a second efficiency that is thephotoelectric conversion efficiency of the photoelectric conversion unitwhen the second voltage is being supplied.

According to the configuration of item 42, an effect that is similar tothat of item 23 can be obtained.

[Item 43]

The camera system according to item 42,

in which the first voltage is a voltage within the first voltage range,and the second voltage is a voltage within the second voltage range.

According to the configuration of item 43, an effect that is similar tothat of item 24 can be obtained.

[Item 44]

The camera system according to item 43,

in which a ratio of the second voltage with respect to the first voltageis greater than a ratio of the second efficiency with respect to thefirst efficiency.

[Item 45]

The camera system according to item 44,

in which the ratio of the second efficiency with respect to the firstefficiency is 1.25 or more.

[Item 46]

The camera system according to item 42,

in which the first voltage and the second voltage are voltages withinthe second voltage range.

According to the configuration of item 46, an effect that is similar tothat of item 27 can be obtained.

[Item 47]

The camera system according to item 46,

in which the ratio of the second efficiency with respect to the firstefficiency is 1 or more and 1.25 or less.

[Item 48]

The camera system according to any one of items 31 to 47,

further provided with a charge accumulation unit that is coupled to thesecond electrode, and temporarily accumulates charges collected by thesecond electrode,

in which a potential of the charge accumulation unit increases togetherwith accumulation of charges in the charge accumulation unit.

According to the configuration of item 48, an effect that is similar tothat of item 29 can be obtained.

[Item 49]

The camera system according to any one of items 31 to 48,

in which the imaging device includes a plurality of pixels each having aphotoelectric conversion unit and an output circuit,

the plurality of pixels include a first pixel and a second pixel that isarranged adjacent to the first pixel, and

the imaging device is further provided with a third electrode that islocated between the second electrode of the first pixel and the secondelectrode of the second pixel, and is electrically insulated from thesecond electrode of the first pixel and the second electrode of thesecond pixel.

According to the configuration of item 49, an effect that is similar tothat of item 30 can be obtained.

[Item 50]

A driving method of an imaging device that has a photoelectricconversion unit that includes a first electrode, a second electrode, anda photoelectric conversion layer located between the first electrode andthe second electrode,

in which, in a case where a quantity of light incident on thephotoelectric conversion unit is greater than or equal to apredetermined quantity of light, a voltage is applied to one of thefirst electrode and the second electrode in such a way that a potentialdifference between the first electrode and the second electrode becomesa first potential difference, and,

in a case where the quantity of light incident on the photoelectricconversion unit is less than the predetermined quantity of light, avoltage is applied to the one of the first electrode and the secondelectrode in such a way that the potential difference between the firstelectrode and the second electrode becomes a second potential differencethat is greater than the first potential difference.

According to the configuration of item 50, a state in which it appearsas if an ND filter has been inserted can be realized by means ofelectrical control.

[Item 51]

The driving method of an imaging device according to item 50,

in which, in a case where a quantity of light incident on thephotoelectric conversion unit is greater than or equal to thepredetermined quantity of light, a first voltage is applied to one ofthe first electrode and the second electrode, and,

in a case where the quantity of light incident on the photoelectricconversion unit is less than the predetermined quantity of light, asecond voltage that is higher than the first voltage is applied to theone of the first electrode and the second electrode.

According to the configuration of item 51, an effect that is similar tothat of item 17 can be obtained.

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the drawings. It should be noted that theembodiments described hereinafter all represent general or specificexamples. The numerical values, the shapes, the materials, theconstituent elements, the arrangement of the constituent elements, themode of connection, the steps, and the order of the steps and so forthgiven in the following embodiments are examples and are not intended torestrict the present disclosure. The various aspects described in thepresent specification may be combined with each other provided there areno resulting inconsistencies. Furthermore, from among the constituentelements in the following embodiments, constituent elements that are notmentioned in the independent claims indicating the most significantconcepts are described as optional constituent elements. In thefollowing description, constituent elements having substantially thesame functions are denoted by common reference characters, anddescriptions thereof are sometimes omitted. Furthermore, some elementsare sometimes not depicted to avoid the drawings becoming overlycomplicated.

First Embodiment

FIG. 1 schematically depicts a configuration of an imaging deviceaccording to a first embodiment of the present disclosure. An imagingdevice 100A depicted in FIG. 1 has a plurality of pixels Px eachincluding in a portion thereof a photoelectric conversion unit supportedon a semiconductor substrate 110. Although not depicted in FIG. 1 , thesemiconductor substrate 110 has a plurality of output circuits formedrespectively corresponding to the pixels Px.

The plurality of pixels Px are arranged two-dimensionally, for example,on the semiconductor substrate 110, and thereby form an imaging region.The quantity and arrangement of the pixels Px are not restricted to theexample depicted in FIG. 1 and are arbitrary. For example, by arrangingthe plurality of pixels Px one-dimensionally, the imaging device 100Acan be used as a line sensor.

As described in detail hereinafter with reference to the drawings, thephotoelectric conversion unit of each pixel Px has a pixel electrode, atransparent opposite electrode, and a photoelectric conversion layersandwiched between these electrodes. Typically, a plurality of pixelelectrodes are arranged in the imaging region corresponding to thepixels Px, whereas an opposite electrode is provided in the form of asingle electrode layer that is contiguous among the plurality of pixelsPx. That is, typically, the potential of the opposite electrode iscommon among the plurality of pixels Px. Similarly for the photoelectricconversion layer, a contiguous single photoelectric conversion structurecan be shared among the plurality of pixels Px. In other words, thephotoelectric conversion unit of each pixel Px includes part of a singletransparent electrode that is contiguous among the plurality of pixelsPx and part of a contiguous single photoelectric conversion structure.

In the configuration exemplified in FIG. 1 , the imaging device 100Aincludes a row scanning circuit 120 that is coupled to each pixel Px viarow signal lines Ri, and a detection circuit 130A that is coupled toeach pixel Px via output signal lines S_(j). Here, the subscript m and nappended to the reference characters in FIG. 1 independently representan integer greater than or equal to 1. The row signal lines R_(i) areprovided for each row of the plurality of pixels Px, and are coupled toone or more pixels Px belonging to the same row. In FIG. 1 , forsimplicity, the row signal lines R_(i) are representatively depicted assignal lines coupled to the row scanning circuit 120; however, it isalso possible for two or more signal lines to be provided for each rowof the plurality of pixels Px. The output signal lines S_(j) areprovided for each column of the plurality of pixels Px, and are coupledto the output circuit of one or more pixels Px belonging to the samerow. As depicted, each of the output signal lines S_(j) is coupled tothe detection circuit 130A.

Typically, the detection circuit 130A includes in a portion thereof acircuit for carrying out noise-suppression signal processing representedby correlated double sampling, analog-digital conversion, and the like.Pixel signals that express an image of an object are read to outside ofthe imaging device 100A as an output of the detection circuit 130A.

Here, the detection circuit 130A has the function of detecting the levelof output signals that are read from the pixels Px via the output signallines S_(j). In this example, a reference line 132 is coupled to thedetection circuit 130A. A predetermined voltage V_(ref) is applied tothe reference line 132 during operation. The detection circuit 130A canhave one or more comparators 134 that output comparison results betweenthe voltage level of the reference line 132 and the level of the outputsignals from the pixels Px of each column, in other words, the voltagelevel of each output signal line S_(j), for example. The comparison ofthe voltage levels may be executed by comparing analog values or may beexecuted by comparing digital values.

In the configuration exemplified in FIG. 1 , the imaging device 100Aalso has a voltage supply circuit 150 and a control circuit 160. Thevoltage supply circuit 150 is coupled to a voltage line 152 that iscoupled to the aforementioned opposite electrode, for example, and isthereby coupled to each pixel Px. The voltage supply circuit 150supplies a predetermined voltage via the voltage line 152 to thephotoelectric conversion unit of each pixel Px during operation of theimaging device 100A.

The voltage supply circuit 150 is configured so as to be able to switchbetween and apply two or more different voltages to the voltage line152. The voltage that is output from the voltage supply circuit 150 maybe altered in steps or may be altered continuously. The voltage supplycircuit 150 is not restricted to a specific power source circuit, andmay be a circuit that converts a voltage supplied from a power sourcesuch as a battery into a predetermined voltage, or may be a circuit thatgenerates a predetermined voltage. The voltage supply circuit 150 may bepart of the row scanning circuit 120.

The control circuit 160 receives command data, a clock, and the likesupplied from outside, for example, for the imaging device 100A andcontrols the entirety of the imaging device 100A. The control circuit160 can be realized by means of a microcontroller including one or moreprocessors, for example. The control circuit 160 can include one or morememories. In the configuration exemplified in FIG. 1 , the controlcircuit 160 includes in a portion thereof a memory 162. The memory 162may be provided in the form of a chip or a package separate from theimaging device 100A.

In this example, an image processing circuit 164 is coupled to thecontrol circuit 160. The image processing circuit 164 can be realized bymeans of a digital signal processor (DSP), an image signal processor(ISP), an field-programmable gate array (FPGA), or the like. The imageprocessing circuit 164 may be part of the control circuit 160.

Typically, the control circuit 160 has a timing generator, and suppliesdrive signals to the row scanning circuit 120, the detection circuit130A, the voltage supply circuit 150, and the like. In FIG. 1 , thearrow extending to the control circuit 160 and the arrows extending fromthe control circuit 160 schematically represent an input signal to thecontrol circuit 160 and output signals from the control circuit 160,respectively. Furthermore, in this example, the control circuit 160 isconfigured so as to receive comparison results between the level of theoutput signals from the pixels Px of each column and the voltage levelof the reference line 132 from the detection circuit 130A, and supplydrive signals corresponding to the voltage level comparison results tothe voltage supply circuit 150.

In a case where, for example, the level of the output signals detectedby the detection circuit 130A is greater than or equal to the voltagelevel of the reference line 132, on the basis of a drive signal from thecontrol circuit 160, the voltage supply circuit 150 applies a voltage tothe voltage line 152 such that a potential difference applied betweenthe opposite electrode and the pixel electrode of the photoelectricconversion units becomes a first potential difference. In a case wherethe level of the output signals detected by the detection circuit 130Ais lower than the voltage level of the reference line 132, a voltage isapplied to the voltage line 152 such that the potential differenceapplied between the opposite electrode and the pixel electrode becomes asecond potential difference that is greater than the first potentialdifference. The voltage supply circuit 150, for example, applies a firstvoltage V1 to the voltage line 152 in a case where the level of theoutput signals detected by the detection circuit 130A is greater than orequal to the voltage level of the reference line 132, and applies asecond voltage V2 that is higher than the first voltage V1 in a casewhere the level of the output signals detected by the detection circuit130A is lower than the voltage level of the reference line 132.Typically, in a case where the illuminance on the photoelectricconversion units is comparatively high, the level of the output signalsfrom the detection circuit 130A is greater than or equal to the voltagelevel of the reference line 132. That is, in the present embodiment, thepotential difference applied between the opposite electrode and thepixel electrode of the photoelectric conversion units is controlled bychanging the voltage applied to the opposite electrode, for example, ofthe photoelectric conversion units in accordance with the illuminance onthe photoelectric conversion units.

In a case where the level of the output signals detected by thedetection circuit 130A is greater than or equal to the voltage level ofthe reference line 132, the relatively low first voltage V1 is appliedto the voltage line 152, for example. In this kind of mode, in asituation where the illuminance is high, the voltage supplied to thephotoelectric conversion units is reduced dynamically. Therefore, powerconsumption can be reduced compared to a configuration in which acomparatively high voltage of approximately 10 V is applied to thephotoelectric conversion units regardless of the environment in whichphotographing is carried out. However, in a case where the illuminanceon the photoelectric conversion units is comparatively low, therelatively high second voltage V2 is applied to the photoelectricconversion unit. As described in detail hereinafter, the photoelectricconversion units of the pixels Px can have photoelectric conversioncharacteristics in which the photoelectric conversion efficiencyincreases in accordance with an increase in a bias voltage between theopposite electrode and the pixel electrode. In this case, thesensitivity of the pixels Px can be increased by applying the relativelyhigh second voltage V2 to the photoelectric conversion units via thevoltage line 152 to increase the potential difference between theopposite electrode and the pixel electrode. In other words, thesensitivity of the pixels Px increases in a dark environment, andphotographing at a high sensitivity becomes possible. In this way,according to the embodiments of the present disclosure, sensitivity isadjusted by means of electrical control in accordance with theilluminance, and therefore the effect of suppressing power consumptioncan be obtained while enabling photographing at a sensitivity thatcorresponds to the environment in which photographing is carried out.

The function of the control circuit 160 may be realized by means of acombination of a general-purpose processing circuit and software, or maybe realized by means of hardware specifically for this kind ofprocessing. It should be noted that, in the example depicted in FIG. 1 ,the row scanning circuit 120, the detection circuit 130A, the voltagesupply circuit 150, and the control circuit 160 are integrally formed onthe semiconductor substrate 110 on which the plurality of pixels Px arearranged. For example, the control circuit 160 can be an integratedcircuit formed on the semiconductor substrate 110. Due to these circuitsbeing arranged on the semiconductor substrate 110 on which the outputcircuits of each pixel Px are formed, it becomes possible to integrallyform these circuits on the semiconductor substrate 110 together with theoutput circuits of each pixel Px, by applying a process that is similarto the process of forming the output circuits of each pixel Px. However,it is not essential for all of these circuits to be integrally formed onthe semiconductor substrate 110 together with the output circuits ofeach pixel Px. It is also possible for some or all of these circuits tobe arranged on a substrate that is different from the semiconductorsubstrate 110 on which the output circuits of each pixel Px are formed.In this case, the imaging device 100A can be provided in the form of apackage in which the semiconductor substrate 110 on which the pluralityof pixels Px are formed, the row scanning circuit 120, the detectioncircuit 130A, the voltage supply circuit 150, and the control circuit160 are integrated.

In the aforementioned example, the control circuit 160 detects the levelof the output signals from each pixel Px by means of the detectioncircuit 130A, and determines whether the quantity of light incident onthe photoelectric conversion units is greater than or equal to apredetermined quantity of light by means of a comparison based on thevoltage level of the reference line 132. In other words, the controlcircuit 160 executes a determination in which the voltage level of thereference line 132 is used as a threshold value. However, the method ofdetermining whether the quantity of light incident on photoelectricconversion units is greater than or equal to the predetermined quantityof light is not restricted to this example.

For example, the detection circuit 130A may be configured so as toinclude an analog-digital conversion circuit and output digital datathat expresses the magnitude of the voltages of the output signal linesS_(j) detected, to the control circuit 160 or the image processingcircuit 164. In this case, a threshold value for determining whether thequantity of light incident on photoelectric conversion units is greaterthan or equal to the predetermined quantity of light can be stored inadvance in the memory 162, for example. In a case where, for example, adigital value received from the detection circuit 130A is greater thanor equal to the threshold value retained in the memory 162, the controlcircuit 160 determines that the quantity of light incident on thephotoelectric conversion units is greater than or equal to thepredetermined quantity of light. In addition, the control circuit 160executes control in which a voltage is applied to the voltage line 152to cause the potential difference between the opposite electrode and thepixel electrode to be a first potential difference that is relativelysmall. For example, the control circuit 160 causes the voltage supplycircuit 150 to be driven in such a way that the relatively low firstvoltage V1 is applied to the voltage line 152.

(Exemplary Configuration of Pixels Px)

FIG. 2 depicts an exemplary circuit configuration of the imaging device100A. Four pixels are extracted from the plurality of pixels Px includedin the imaging region depicted in FIG. 1 and schematically depicted inFIG. 2 .

Each pixel Px includes a photoelectric conversion unit 10 and an outputcircuit 20 that is coupled to the photoelectric conversion unit 10. Inthe configuration exemplified in FIG. 2 , the output circuit 20 includesa signal detection transistor 22, an address transistor 24, and a resettransistor 26. The signal detection transistor 22, the addresstransistor 24, and the reset transistor 26 are typically field-effecttransistors formed on the semiconductor substrate 110, and, hereinafter,an example is described in which N-channel MOS transistors are used asthese transistors.

As schematically depicted in FIG. 2 , the photoelectric conversion unit10 includes an opposite electrode 11 serving as a first electrode, apixel electrode 12 serving as a second electrode, and a photoelectricconversion layer 13 sandwiched between the opposite electrode 11 and thepixel electrode 12. The opposite electrode 11 is transparent. It shouldbe noted that the word “transparent” in the present specification meansthat at least a portion of light of a wavelength that can be absorbed bythe photoelectric conversion layer 13 is transmitted, and it is notessential for light to be transmitted across the entire wavelength rangeof visible light.

As depicted, the opposite electrode 11 of each pixel Px is coupled tothe voltage line 152. Consequently, the voltage supply circuit 150 isable to selectively apply the first voltage V1 or the second voltage V2,for example, collectively to the opposite electrodes 11 of the pluralityof pixels Px via the voltage line 152. In FIG. 2 , it is depicted as ifthe voltage line 152 is coupled to each opposite electrode 11 of theplurality of pixels Px. However, typically, the opposite electrode 11 ofeach pixel Px is a single transparent electrode that is contiguous amongthe plurality of pixels Px, and it is not necessary for the voltage line152 to be a wire that branches into a plurality.

Meanwhile, the pixel electrode 12 is provided electrically isolated ineach pixel Px. As depicted, the pixel electrode 12 of each pixel Px iscoupled to the gate of the signal detection transistor 22 of thecorresponding output circuit 20. The source of the signal detectiontransistor 22 is coupled to the corresponding output signal line S_(j)via the address transistor 24. The drain of the signal detectiontransistor 22 is coupled to a power source line 32. The power sourceline 32 functions as a source-follower power source due to a powersource voltage VDD of approximately 3.3 V being applied duringoperation.

The gate of the address transistor 24 is coupled to a row signal lineR_(i). The row scanning circuit 120 can switch the address transistors24 between on and off and can read signals from the pixels Px of aselected row to an output signal line S_(j), by controlling the voltagelevels applied to the row signal lines Ri.

In this example, the output circuit 20 includes the reset transistor 26.One of the source and drain of the reset transistor 26 is coupled to anode FD. The node FD electrically connects the photoelectric conversionunit 10 to the gate of the signal detection transistor 22. The other ofthe source and drain of the reset transistor 26 is coupled to a resetvoltage line 36. A predetermined reset voltage V_(RST) is applied to thereset voltage line 36 during operation of the imaging device 100A.Typically, as depicted, a reset signal line 46 is coupled in common tothe gates of the reset transistors 26 of the plurality of pixels Pxbelonging to the same row.

In this example, the reset signal line 46 is coupled to the row scanningcircuit 120. The row scanning circuit 120 switches the reset transistors26 on in units of rows of the plurality of pixels Px by controlling thevoltage level applied to the reset signal line 46. Thus, the potentialof the node FD of a pixel Px in which the reset transistor 26 has beenswitched on can be reset to V_(RST). If the voltage applied to theopposite electrode 11 of each pixel Px from the voltage supply circuit150 is taken as V1 or V2, a bias voltage that is applied between thepixel electrode 12 and the opposite electrode 11 immediately after areset is (V1−V_(RST)) or (V2−V_(RST)). As described hereinafter, in theembodiments of the present disclosure, specific values of these voltagescan be selected in such a way that (V1−V_(RST))>0 and (V2−V_(RST))>0.

FIG. 3A depicts an exemplary device structure of a pixel Px. Thesemiconductor substrate 110 has impurity regions 111 to 115 and elementisolation regions 116. The element isolation regions 116 electricallyisolate the output circuit 20 provided in each pixel Px, between thepixels Px. Hereinafter, a P-type silicon substrate is given as anexample of the semiconductor substrate 110. The impurity regions 111 to115 are typically N-type diffusion regions. The semiconductor substrate110 may be an insulating substrate having a semiconductor layer providedon the surface thereof or the like.

The signal detection transistor 22 includes the impurity regions 113 and114 from among the impurity regions 111 to 115, a gate insulation layer22 g on the semiconductor substrate 110, and a gate electrode 22 e onthe gate insulation layer 22 g. The impurity region 113 functions as adrain region of the signal detection transistor 22. The impurity region114 functions as a source region of the signal detection transistor 22.In the configuration depicted, the address transistor 24 shares theimpurity region 114 with the signal detection transistor 22. The addresstransistor 24 includes a gate insulation layer 24 g on the semiconductorsubstrate 110, a gate electrode 24 e on the gate insulation layer 24 g,and the impurity region 115. The impurity region 115 functions as asource region of the address transistor 24.

The reset transistor 26 includes the impurity regions 111 and 112, agate insulation layer 26 g on the semiconductor substrate 110, and agate electrode 26 e on the gate insulation layer 26 g. Although notdepicted in FIG. 3A, the aforementioned reset voltage line 36 is coupledto the impurity region 112. It should be noted that the aforementionedpower source line 32 is coupled to the impurity region 113 serving asthe drain region of the signal detection transistor 22. Anaforementioned output signal line S_(j) is coupled to the impurityregion 115 serving as the source region of the address transistor 24. Asschematically depicted in FIG. 3A, an element isolation region 116 isprovided between the reset transistor 26 and the signal detectiontransistor 22.

An interlayer insulating layer 50 covers the signal detection transistor22, the address transistor 24, and the reset transistor 26 formed on thesemiconductor substrate 110. The photoelectric conversion unit 10 ofeach pixel Px is supported by the interlayer insulating layer 50. Theinterlayer insulating layer 50 includes a plurality of insulating layerseach formed from silicon dioxide, for example.

The opposite electrode 11 of the photoelectric conversion unit 10 islocated at the side where light from an object is incident, and isformed from a transparent electrically conductive material such as ITO.As mentioned above, the opposite electrode 11 is typically provided inthe form of a single electrode layer that is contiguous across theplurality of pixels Px. An optical filter 14 such as a color filter, amicrolens 16 may be arranged on a main surface, at the opposite side ofthe opposite electrode 11 to the photoelectric conversion layer 13.

The photoelectric conversion layer 13 located between the oppositeelectrode 11 and the pixel electrode 12 is formed from an organicmaterial or an inorganic material such as amorphous silicon, andreceives incident light via the opposite electrode 11 and causesexcitons to be generated. The photoelectric conversion layer 13 mayinclude a layer configured from an organic material and a layerconfigured from an inorganic material. Similar to the opposite electrode11, the photoelectric conversion layer 13 is typically provided in theform of a single photoelectric conversion structure that is contiguousacross the plurality of pixels Px.

The pixel electrode 12 is located nearer the semiconductor substrate 110than the photoelectric conversion layer 13, and is spatially separatedfrom the pixel electrodes 12 of other adjacent pixels Px and is therebyelectrically isolated therefrom. The pixel electrode 12 can be formedfrom a metal such as aluminum or copper, a metal nitride, polysiliconimparted with conductivity due to being doped with an impurity, forexample.

Each pixel Px has a conductive structure 52 inside the interlayerinsulating layer 50. The conductive structure 52 electrically connectsthe pixel electrode 12 to the output circuit 20 including the signaldetection transistor 22. The conductive structure 52 includes a viaformed from a metal such as copper, a plug formed from polysilicon, orthe like, and electrically connects the pixel electrode 12 and theimpurity region 111 formed in the semiconductor substrate 110 to eachother, as schematically depicted in FIG. 3A. This conductive structure52 also connects the pixel electrode 12 to the gate electrode 22 e ofthe signal detection transistor 22. In other words, the output circuit20 outputs a signal that corresponds to the potential of the pixelelectrode 12 to the corresponding output signal line S_(j) by means of asource follower that includes the signal detection transistor 22.

During operation, a potential difference ΔV is applied between theopposite electrode 11 and the pixel electrode 12 as schematicallydepicted in FIG. 3A, due to a predetermined voltage being applied to theopposite electrode 11 from the voltage supply circuit 150 via thevoltage line 152. Here, the voltage supply circuit 150, based on thepixel electrode 12, applies a voltage to the opposite electrode 11 suchthat the potential of the opposite electrode 11 becomes higher than thepotential of the pixel electrode 12. By making the potential of theopposite electrode 11 higher than the potential of the pixel electrode12, from among positive and negative charges generated in thephotoelectric conversion layer 13 due to the incidence of light, chargeshaving a positive polarity, such as electron holes, can be collected bythe pixel electrode 12 as signal charges. Hereinafter, unless otherwisespecified, an example in which electron holes are used as signal chargeswill be described. It should be noted that, in the example depicted inFIG. 3A, an electron blocking layer 13 e is arranged between thephotoelectric conversion layer 13 and the pixel electrode 12, and theinjection of electrons into the pixel electrode 12 from thephotoelectric conversion layer 13 is suppressed. The electron blockinglayer 13 e may have a photoelectric conversion function.

In a typical embodiment of the present disclosure, in either of a statein which the first voltage V1 is applied to the voltage line 152 fromthe voltage supply circuit 150 and a state in which the second voltageV2 is applied to the voltage line 152 from the voltage supply circuit150, the potential of the opposite electrode 11 is higher than thepotential of the pixel electrode 12. It should be noted that thepotential of the pixel electrode 12 is determined according to theaforementioned reset voltage V_(RST) that is supplied via the resettransistor 26. Consequently, in a typical embodiment of the presentdisclosure, (V1−V_(RST))>0 and (V2−V_(RST))>0 are satisfied. A positivevoltage in the vicinity of 0 V or 0V, for example, is used as the resetvoltage V_(RST).

The impurity region 111 is coupled to the conductive structure 52 in theinterlayer insulating layer 50. A P-N junction formed in thesemiconductor substrate 110 by the impurity region 111 functions as acharge accumulation capacitance in which positive charges, such aselectron holes, collected by the pixel electrode 12 are temporarilyaccumulated. In a typical embodiment of the present disclosure, electronholes are used as signal charges, and therefore the potential of theimpurity region 111 serving as a charge accumulation unit increasestogether with the accumulation of signal charges in the impurity region111.

By applying a voltage to the opposite electrode 11 such that thepotential of the opposite electrode 11 becomes lower than that of thepixel electrode 12, it goes without saying that it is also possible forelectrons to be used as signal charges, for example. FIG. 3B is aschematic cross-sectional view for describing an operation of the pixelsPx in a case where electrons are used as signal charges. In a case wherenegative charges are to be collected by the pixel electrode 12, forexample, it is sufficient that a voltage is applied to the oppositeelectrode 11 such that the potential of the pixel electrode 12 becomeshigher than the potential of the opposite electrode 11. In theconfiguration exemplified in FIG. 3B, an electron-hole blocking layer 13h is arranged between the photoelectric conversion layer 13 and thepixel electrode 12, and the injection of electron holes into the pixelelectrode 12 from the photoelectric conversion layer 13 is suppressed.

With this case also, the control circuit 160 causes a predeterminedvoltage to be output from the voltage supply circuit 150 such that thepotential difference applied between the opposite electrode 11 and thepixel electrode 12 becomes the first potential difference, in a casewhere the level of the output signals detected by the detection circuit130A is greater than or equal to the voltage level of the reference line132, for example. Furthermore, in a case where the level of the outputsignals detected by the detection circuit 130A is less than the voltagelevel of the reference line 132, the control circuit 160 causes avoltage to be output from the voltage supply circuit 150 such that thepotential difference applied between the opposite electrode 11 and thepixel electrode 12 becomes a second potential difference that is greaterthan the first potential difference. It should be noted that, in aconfiguration in which electrons are accumulated as signal charges, thepotential of the impurity region 111 serving as a charge accumulationunit decreases together with the accumulation of signal charges in theimpurity region 111.

(Exemplary Photoelectric Conversion Characteristics of PhotoelectricConversion Layer)

Here, a description will be given regarding a relationship between thephotoelectric conversion characteristics of the photoelectric conversionlayer 13 and the voltage supplied to the voltage line 152 by the voltagesupply circuit 150. Hereinafter, unless otherwise specified, an examplein which electron holes are used as signal charges will be described.

FIG. 4 depicts a typical example of the photoelectric conversioncharacteristics of the photoelectric conversion layer 13. In FIG. 4 ,the horizontal axis represents the potential difference ΔV appliedbetween the opposite electrode 11 and the pixel electrode 12, and thevertical axis represents the photoelectric conversion efficiency η ofthe photoelectric conversion layer 13. Here, the photoelectricconversion efficiency η means the ratio per unit second of the number ofcharges collected by the pixel electrode 12, with respect to the numberof photons incident on the photoelectric conversion unit 10, for onepixel Px. It should be noted that the number of charges is a number thatis measured with elementary electric charge as a unit.

As exemplified in FIG. 4 , in the embodiments of the present disclosure,a change is indicated in which the photoelectric conversion efficiency ηof the photoelectric conversion layer 13 generally increases with anupwardly convex curved form with respect to an increase in the potentialdifference ΔV applied between the opposite electrode 11 and the pixelelectrode 12. A photoelectric conversion layer having photoelectricconversion characteristics such as those depicted in FIG. 4 can berealized by using organic photoelectric conversion materials that aregenerally applied in the forming of an organic photoelectric conversionfilm and combinations thereof.

In the example depicted in FIG. 4 , the photoelectric conversionefficiency r_(i) indicates a comparatively sharp increase with respectto a change in the potential difference ΔV in a voltage region having acomparatively low potential difference ΔV of approximately 0 to 3 V, andindicates a comparatively gentle increase with respect to a change inthe potential difference ΔV in a voltage region having a comparativelyhigh potential difference ΔV of approximately 3 V or more. In thepresent specification, a voltage range in which the photoelectricconversion efficiency η indicates a comparatively sharp increase withrespect to a change in the potential difference ΔV applied between theopposite electrode 11 and the pixel electrode 12 is referred to as afirst voltage range, and a voltage range in which the photoelectricconversion efficiency η indicates a comparatively gentle increase withrespect to a change in the potential difference ΔV is referred to as asecond voltage range.

The first voltage range can be defined as a voltage range in which thepotential difference ΔV applied between the opposite electrode 11 andthe pixel electrode 12, in other words, the rate of change in thephotoelectric conversion efficiency of the photoelectric conversion unit10 with respect to the bias voltage, indicates a larger value than whenthe bias voltage is in the second voltage range. The specific ranges ofthe first voltage range and the second voltage range may differdepending on the use of the imaging device 100A, the material of thephotoelectric conversion layer 13, and the like, but can be defined asdescribed hereinafter, for example. In a graph of the photoelectricconversion efficiency η of the photoelectric conversion unit 10 withrespect to the bias voltage between the opposite electrode 11 and thepixel electrode 12, as indicated by a dashed line in FIG. 4 , a tangentT1 is drawn at a point where the photoelectric conversion efficiency ηrises from 0. Furthermore, a tangent T2 is drawn at a pointcorresponding to the largest value during operation for the biasvoltage. The value of the bias voltage at an intersecting point of thesetangents T1 and T2 is taken as Vt, and a voltage range that is less thanVt is taken as the first voltage range.

In the example depicted in FIG. 4 , the value of the potentialdifference ΔV where the photoelectric conversion efficiency η rises from0 is 0 V, and the largest value of the bias voltage during operation isΔV=12 V. The X coordinate of the intersecting point of the tangents atthese points is approximately 3 V, and consequently, as depicted in FIG.4 , a voltage region of approximately 0 V or more and less than 3 V canbe taken as the first voltage range, and a voltage region ofapproximately 3 V or more and 12 V or less can be taken as the secondvoltage range.

However, it is also possible that there is no intersection between thetangent T1 at the point where the photoelectric conversion efficiency ηrises from 0 and the tangent T2 at the point corresponding to thelargest value during operation for the bias voltage, in a case where acharacteristic curve in which the photoelectric conversion efficiency ηrises gently from 0 is obtained in a region in which the potentialdifference ΔV is comparatively small, as exemplified in FIG. 5 . In sucha case, in a graph of the photoelectric conversion efficiency η, asindicated by a dashed line in FIG. 5 , a tangent T3 is drawn at a pointR where the value of the photoelectric conversion efficiency η becomes0.06, and an intersecting point between this tangent T3 and the tangentT2 is obtained. Then, the value of the bias voltage at the intersectingpoint of the tangents T3 and T2 may be taken as Vt, and a voltage rangethat is less than Vt may be taken as the first voltage range.

It should be noted that the aforementioned value 0.06 for thephotoelectric conversion efficiency η is a normalized value when thephotoelectric conversion efficiency η at the point corresponding to thelargest value during operation for the bias voltage is taken as 1. Inthe field of digital cameras, ND filters are sometimes combined in adigital camera for photographing with a low shutter speed or the like.The sensitivity realized by means of the value 0.06 for thephotoelectric conversion efficiency η generally corresponds to the casewhere an ND16 filter is applied. Consequently, in a graph of thephotoelectric conversion efficiency η with respect to the potentialdifference ΔV, Vt is obtained using the tangent at the point R where theY coordinate is 0.06, and thus a sensitivity corresponding to a range ofND2 to ND16, for example, can be realized by means of electricalcontrol.

Alternatively, a voltage range in which a change in the photoelectricconversion efficiency η is less than 10% with respect to a change of 1 Vin the bias voltage may be used as the second voltage range. In thiscase, the second voltage range is determined as being a voltage range inwhich (c-b) constituting an increment in the photoelectric conversionefficiency η satisfies the relationship (c-b)<0.1*b when a first pointP(a, b) and a second point Q(a+1, c) are taken on the graph, as depictedin FIG. 6 . Here, “*” in the aforementioned relational expressionrepresents multiplication.

As yet another alternative, the first voltage range or the secondvoltage range can also be determined as described hereinafter. Forexample, in a graph of the photoelectric conversion efficiency η of thephotoelectric conversion unit 10 with respect to the bias voltagebetween the opposite electrode 11 and the pixel electrode 12, a regionin which the photoelectric conversion efficiency η is 0.7 or more mayserve as the second voltage range, as depicted in FIG. 7 . It should benoted that, when a region in which the photoelectric conversionefficiency η is 0.7 or more is defined as the second voltage range,there is an advantage in that it is easy to achieve correspondence withISO numerical values. It is sufficient that specific ranges for thefirst voltage range and the second voltage range are set as appropriatein accordance with the use of the imaging device 100A or the like.

In a typical embodiment of the present disclosure, as the aforementionedfirst voltage V1 and second voltage V2, voltages are used with which thephotoelectric conversion efficiency η produced when the first voltage V1is supplied to the photoelectric conversion unit 10 is lower than whenthe second voltage V2 is supplied to the photoelectric conversion unit10. As mentioned above, the photoelectric conversion efficiency η in thephotoelectric conversion layer 13, typically, generally increases in amonotonous manner with respect to an increase in the potentialdifference ΔV applied between the opposite electrode 11 and the pixelelectrode 12. Consequently, for example, a voltage within the firstvoltage range can be adopted as the first voltage V1, and a voltagewithin the second voltage range can be adopted as the second voltage V2.Hereinafter, first, a description will be given regarding an operationexample of the imaging device 100A when a voltage within the firstvoltage range is used as the first voltage V1 and a voltage within thesecond voltage range is used as the second voltage V2.

(First Operation Example of Imaging Device 100A)

Here, the photoelectric conversion efficiency η in the photoelectricconversion layer 13 is assumed to indicate a change such as thatdepicted in FIG. 4 with respect to an increase in the potentialdifference ΔV applied between the opposite electrode 11 and the pixelelectrode 12, and the value Vt of the bias voltage at the aforementionedintersecting point between the tangents T1 and T2 is assumed to be 3 V.At such time, when a voltage region of less than 3 V is taken as thefirst voltage range and a voltage region of 3 V or more and 12 V or lessis determined as the second voltage range, for example, a voltage of 2 Vcan be used as the first voltage V1 and a voltage of 6 V can be used asthe second voltage V2, for example.

In a case where definitions such as these are adopted for the firstvoltage range and the second voltage range, the ratio of thephotoelectric conversion efficiency η produced when the second voltageV2 is applied to the opposite electrode 11 with respect to the value ofthe photoelectric conversion efficiency η produced when the firstvoltage V1 is applied to the opposite electrode 11 is, typically, 1.25or more and 100 or less. In this example, the photoelectric conversionefficiency η produced when the first voltage V1 is applied to theopposite electrode 11 is approximately 0.55, the value of thephotoelectric conversion efficiency η produced when the second voltageV2 is applied is approximately 0.87, and the value of the ratio forthese values for η is approximately 1.58. It should be noted that 3,which is the value of the ratio (V2/V1) of the second voltage V2 withrespect to the first voltage V1 is greater than the aforementioned ratiovalue 1.58 in relation to η.

FIG. 8 is a schematic flowchart depicting a first exemplary operation ofthe imaging device 100A. In the example depicted in FIG. 8 , first, itis determined whether or not the quantity of light incident on thephotoelectric conversion units 10 is greater than or equal to apredetermined quantity of light (step S1). For example, the level of thesignals that are output to the output signal lines S_(j) from the outputcircuits 20 is detected by the detection circuit 130A. In a case wherethe detected level is greater than or equal to the voltage level of thereference line 132 serving as a threshold value, it can be determinedthat the quantity of light incident on the photoelectric conversionunits 10 is greater than or equal to the predetermined quantity oflight. The level of the signals from the output circuits 20 may bedetected by, for example, when the user has half-pressed a releasebutton, switching the address transistors 24 of some of the pixels Px toon, and causing a voltage that corresponds to the illuminance to beoutput from the output circuits 20. Alternatively, the level of thesignals detected by the detection circuit 130A in, for example, theframe immediately preceding the frame in which images are to be acquiredfrom thereon may be used.

It goes without saying that the method of determining whether or not thequantity of light incident on the photoelectric conversion units 10 isgreater than or equal to the predetermined quantity of light is notrestricted to a specific method, and various methods can be adopted. Forexample, the level of the signals detected by the detection circuit 130Amay be converted into a digital value by an analog-digital conversioncircuit, and whether or not the quantity of light incident on thephotoelectric conversion units 10 is greater than or equal to thepredetermined quantity of light may be determined by comparison with athreshold value stored in advance in the memory 162. Whether or not thequantity of light incident on the photoelectric conversion units 10 isgreater than or equal to the predetermined quantity of light can bedetermined by the control circuit 160 or the image processing circuit164, for example. The control circuit 160 may include a logic circuitformed on the semiconductor substrate 110. Whether or not the quantityof light incident on the photoelectric conversion units 10 is greaterthan or equal to the predetermined quantity of light may be determinedby an ISP, for example, arranged outside of the imaging device 100A.

In a case where it has been determined that the quantity of lightincident on the photoelectric conversion units 10 is greater than orequal to the predetermined quantity of light, a voltage is applied tothe photoelectric conversion units 10 in such a way that the potentialdifference between the opposite electrode 11 and the pixel electrode 12becomes the first potential difference (step S2). The control circuit160 supplies a drive signal to the voltage supply circuit 150, and, forexample, causes the first voltage V1 to be applied to the voltage line152 from the voltage supply circuit 150. As depicted in FIG. 4 , in astate in which the first voltage V1 is applied to the opposite electrode11, the photoelectric conversion efficiency of the photoelectricconversion units 10 is relatively low, and, consequently, each pixel Pxof the imaging device 100A enters a state in which the sensitivity hasrelatively decreased. As mentioned above, a case where the quantity oflight incident on the photoelectric conversion units 10 is greater thanor equal to the predetermined quantity of light corresponds to a casewhere the illuminance on the photoelectric conversion unit 10 is high.In other words, in this example, the sensitivity of the pixels Pxdecreases automatically in the case where the illuminance on thephotoelectric conversion units 10 is high. In other words, it can besaid that a state in which it appears as if an ND filter has beenmechanically inserted is realized by means of electrical control.Consequently, the user of the imaging device 100A can more easily carryout photographing that is adapted to the environment.

In this way, it becomes possible to realize an ND filter functionimplemented by means of electrical control, by controlling the voltageapplied to the photoelectric conversion units 10 from the voltage supplycircuit 150. Consequently, it is no longer necessary to prepare aplurality of ND filters even for a photographing scene for which it hasheretofore been necessary for one appropriate ND filter to be selectedand used from among a plurality of ND filters, and an effect ofsimplifying photographic equipment can be obtained. According to theembodiments of the present disclosure, it becomes possible to implementcontinuous alteration, in other words, stepless control, of sensitivitythat was not possible with a conventional silicon image sensor, and itis possible to extend the degree of freedom of photographing thatcorresponds to the scene.

FIGS. 9 and 10 are schematic cross-sectional views for describing achange in the photoelectric conversion efficiency η with respect to achange in illuminance, when a voltage of 2 V is applied as the firstvoltage V1 to the opposite electrode 11. During operation, the potentialdifference ΔV is applied between the opposite electrode 11 and the pixelelectrode 12. The reset voltage V_(RST) is a voltage in the vicinity of0 V, for example, and consequently, in a state in which the voltagesupply circuit 150 is supplying the first voltage V1, the photoelectricconversion layer 13 is in a state in which a potential difference ofapproximately 2 V is applied, as schematically depicted in FIG. 9 .

When light is incident on the photoelectric conversion layer 13 andcharges are generated inside the photoelectric conversion layer 13,these charges move according to the electric field between the oppositeelectrode 11 and the pixel electrode 12. As schematically depicted inFIG. 9 , positive charges are accumulated in the impurity region 111serving as a charge accumulation unit via the conductive structure 52,and negative charges are discharged to the voltage line 152 from thephotoelectric conversion layer 13 via the opposite electrode 11.

In a state in which the first voltage V1 is being supplied from thevoltage supply circuit 150, in other words, a state in which thepotential difference ΔV between the opposite electrode 11 and the pixelelectrode 12 is relatively small, there are few charge pairs generatedby photoelectric conversion, and there is also a high probability ofrecombination occurring before positive charges reach the pixelelectrode 12. Furthermore, for positive charges, it becomes difficult toovercome a potential barrier formed by the electron blocking layer 13 e.Therefore, when compared in the same illuminance, there are fewer signalcharges accumulated in the impurity region 111 than when a relativelylarge potential difference ΔV is applied between the opposite electrode11 and the pixel electrode 12. That is, a state is entered in which thesensitivity of the pixels Px has decreased.

When the accumulation of signal charges in the impurity region 111continues, since positive charges are used as signal charges here, thepotential of the impurity region 111 gradually increases. Therefore, theeffective bias voltage according to the photoelectric conversion layer13 is less than the actual value of the first voltage V1, and theeffective bias voltage decreases as more signal charges are accumulatedin the impurity region 111. In other words, the sensitivity of thepixels Px decreases as the signal charges are accumulated in theimpurity region 111.

Here, as schematically depicted by the arrows hν in FIG. 10 , it isassumed that the illuminance on the photoelectric conversion unit 10increases in a state in which the first voltage V1 is being suppliedfrom the voltage supply circuit 150. When the signal charges accumulatedin the impurity region 111 increase due to the increase in illuminance,the potential of the impurity region 111 rises, and thus the effectivebias voltage according to the photoelectric conversion layer 13decreases. For example, when the bias voltage has decreased from 2 V to1 V approximately, as is apparent from FIG. 4 , the photoelectricconversion efficiency η decreases from 0.55 to 0.28 approximately, andas a result the sensitivity of the pixels Px decreases further. In otherwords, the effective bias voltage according to the photoelectricconversion layer 13 is changed according to the illuminance while thevoltage applied to the voltage line 152 from the voltage supply circuit150 is constant, and as a result the effect of an expansion in thedynamic range can be obtained. The state in which the first voltage V1in the first voltage range is being supplied from the voltage supplycircuit 150 may be referred to as a sensitivity variable mode.

FIG. 11 is a drawing schematically depicting a typical example of achange in the level of the signal from the output circuit 20, withrespect to a change in the quantity of light incident on thephotoelectric conversion unit 10. From FIG. 11 , in a region in whichthe quantity of light is comparatively small, the level of the signalsindicates a linear change with respect to a change in the quantity oflight, and it is understood that linearity can be ensured. When thequantity of light increases further, the degree of the increase in thelevel of the signals with respect to the increase in the quantity oflight decreases, and a graph depicting a change in the level of thesignals with respect to a change in the quantity of light comes toindicate a change having a curved form. In this way, the level of thesignals automatically decreases in accordance with an increase in thequantity of light, and therefore the dynamic range relating to thedirection in which the illuminance is high is expanded. Using this,compared to a case where the level of the signals changes in a linearform in accordance with an increase in the quantity of light, thedynamic range relating to the direction in which the illuminance is highcan be approximately doubled, for example.

In a region in which the illuminance is even higher, there is anincrease in the deviation from a straight line in a graph depicting achange in the level of the signals with respect to a change in thequantity of light. This is because, as the potential difference ΔVdecreases, effects such as a decrease in charge pairs generated byphotoelectric conversion and an increase in the disappearance of chargepairs due to recombination appear more easily.

However, by obtaining a characteristic curve such as that depicted inFIG. 11 in advance, it becomes possible to carry out an appropriatecorrection to the level of the signals detected by the detection circuit130A. For example, correction coefficients corresponding to quantitiesof light may be stored in the memory 162 in advance in the form of atable, for example, and the pixel value of each pixel Px may bedetermined by multiplying by a correction coefficient. Due to this kindof correction, linearity is compensated, and it becomes possible tofurther expand the dynamic range relating to the direction in which theilluminance is high. For example, compared to the case where the levelof the signals changes in a linear form in accordance with an increasein the quantity of light, the dynamic range relating to the direction inwhich the illuminance is high can be approximately tripled.

A correction for the level of the signals detected can be executed bythe image processing circuit 164. The function of the image processingcircuit 164, similar to the control circuit 160, may be realized bymeans either of a combination of a general-purpose processing circuitand software, and hardware specifically for image processing. Acorrection for the level of the signals detected may be executed by thecontrol circuit 160.

Reference will once again be made to FIG. 8 . In step S1, in a casewhere it has been determined that the quantity of light incident on thephotoelectric conversion units 10 is less than the predeterminedquantity of light, a voltage is applied to the photoelectric conversionunits 10 in such a way that the potential difference between theopposite electrode 11 and the pixel electrode 12 becomes a secondpotential difference that is greater than the first potential difference(step S3). The control circuit 160 supplies a drive signal to thevoltage supply circuit 150, and, for example, causes the second voltageV2, which is higher than the first voltage V1, to be applied to thevoltage line 152 from the voltage supply circuit 150.

When the potential difference ΔV between the opposite electrode 11 andthe pixel electrode 12 increases, the electric field inside thephotoelectric conversion layer 13 increases, and a larger quantity ofpositive charges are collected by the pixel electrode 12, asschematically depicted in FIG. 12 . In other words, the sensitivity ofthe pixels Px obtained when the second voltage V2 is applied to theopposite electrode 11 is in a high state compared to a state in whichthe first voltage V1 is applied to the opposite electrode 11. Here, avoltage of 6 V is used as the second voltage V2. As is apparent withreference to FIG. 4 , the photoelectric conversion efficiency in a statein which the second voltage V2 is applied to the opposite electrode 11is high compared to a state in which the first voltage V1 is applied tothe opposite electrode 11. In the example depicted in FIG. 4 , the valueof the photoelectric conversion efficiency η at such time isapproximately 0.87.

The potential of the impurity region 111 gradually rises due tocontinuation of the accumulation of signal charges in the impurityregion 111, which is the same as when the first voltage V1 is applied tothe opposite electrode 11. Consequently, the effective bias voltageaccording to the photoelectric conversion layer 13 is less than thevalue of the second voltage V2, and can become approximately 5 V, forexample. It should be noted that positive charges produced by the pixelelectrode 12 are no longer collected when the potential of the pixelelectrode 12 exceeds the potential of the opposite electrode 11, andtherefore the potential of the impurity region 111 basically does notexceed the value of the second voltage V2.

FIG. 13 schematically depicts a typical example of a change in the levelof the signals from the output circuits 20, with respect to a change inthe quantity of light incident on the photoelectric conversion units 10,when the second voltage V2 is applied to the opposite electrode 11. FIG.13 also depicts a change in the level of output signals with respect toa change in the quantity of light, when a voltage of 2 V is applied asthe first voltage V1 to the opposite electrode 11. Line G1 in FIG. 13 isthe same as the line depicted in FIG. 11 , and depicts a change in thelevel of the output signals when 2 V is applied to the oppositeelectrode 11. Meanwhile, line G2 in FIG. 13 depicts a change in thelevel of the output signals when 6 V is applied to the oppositeelectrode 11.

As is apparent from FIG. 13 , in a state in which a relatively highvoltage of 6 V, for example, is applied as the second voltage V2 to theopposite electrode 11, the level of the signals from the output circuits20 indicates a linear change with respect to a change in the quantity oflight incident on the photoelectric conversion units 10. In other words,in this example, it is understood that the linearity of the signaloutput with respect to a change in illuminance can be ensured naturallyin an environment in which illuminance is low such as when the secondvoltage V2 is supplied from the voltage supply circuit 150.

In this way, control is carried out in such a way that the first voltageV1 in the first voltage range is supplied to the photoelectricconversion units 10 in an environment in which illuminance iscomparatively high, and the second voltage V2 in the second voltagerange is supplied to the photoelectric conversion units 10 in anenvironment in which illuminance is comparatively low. According to thiskind of control, sensitivity can be dynamically changed according tochanges in illuminance. For example, at the standard setting, the secondvoltage V2 in the second voltage range is used as the voltage suppliedto the photoelectric conversion units 10, and, in an environment inwhich illuminance is comparatively high, the first voltage V1 in thefirst voltage range is used as the voltage supplied to the photoelectricconversion units 10. It thereby becomes possible for sensitivity to bedecreased dynamically. In addition, in a state in which illuminance iscomparatively high and the first voltage V1 in the first voltage rangeis supplied to the photoelectric conversion units 10, when theilluminance further increases, the potential difference ΔV reduces inaccordance with the accumulation of electron holes in the impurityregion 111. As a result, the photoelectric conversion efficiency ηchanges in a further decreasing direction, and therefore the dynamicrange relating to the direction in which the illuminance is high can befurther expanded.

It should be noted that, as exemplified in FIG. 14 , a third electrode15 may be arranged between two pixel electrodes 12 that are adjacent toeach other. As described hereinafter, by controlling the potential ofthe third electrode 15, it is possible to further expand the dynamicrange relating to the direction in which the illuminance is high.

FIG. 14 depicts two pixels Px1 and Px2 that are adjacent to each otherin a row or column, for example, of the plurality of pixels Px.Furthermore, in FIG. 14 , the third electrode 15 is arranged between thepixel electrode 12 of the pixel Px1 and the pixel electrode 12 of thepixel Px2, and in the same layer as these pixel electrodes 12. The thirdelectrode 15 is spatially separated from the pixel electrode 12 of thepixel Px1 and the pixel electrode 12 of the pixel Px2, and is therebyelectrically isolated from these pixel electrodes 12. The thirdelectrode 15 is configured so that a predetermined voltage can beapplied during operation of the imaging device 100A by being coupled toa power source that is not depicted.

FIG. 15 depicts an example of the arrangement relationship between thepixel electrode 12 and the third electrode 15, when seen from theopposite electrode 11 side. In this example, the third electrode 15 hasa rectangular shape surrounding the pixel electrode 12, and is providedin each of the pixel Px1 and the pixel Px2. It should be noted that itis not essential for the third electrode 15 to be arranged separatelyfor each pixel Px. For example, it is also possible for a single thirdelectrode 15 that straddles the plurality of pixels Px to be providedfor each row of the plurality of pixels Px. Furthermore, it is alsopossible for a grid-shaped third electrode 15 to be arranged across theplurality of pixels Px.

When a potential that is lower than that of the opposite electrode 11 isapplied, the pixel electrode 12 collects positive charges in a regionR1, of the photoelectric conversion layer 13, located more or lessdirectly above the pixel electrode 12, as schematically depicted by theshading in FIG. 15 . Similarly, when a potential that is lower than thatof the opposite electrode 11 is applied, the third electrode 15 cancollect positive charges in a region R2, of the photoelectric conversionlayer 13, located more or less directly above the third electrode 15.

Consequently, when the illuminance is high, a voltage that is less thanor equal to the reset voltage V_(RST), for example, is applied to thethird electrode 15 for a potential difference that is greater than orequal to ΔV to be applied to a portion, of the photoelectric conversionlayer 13, located between the opposite electrode 11 and the thirdelectrode 15, and it thereby becomes possible for charges generated nearboundaries of the pixels Px to be preferentially collected by the thirdelectrode 15, as schematically depicted in FIG. 16 . As a result, thenumber of charges that reach the pixel electrode 12 decreases, and theeffective photoelectric conversion efficiency can be further lowered. Inother words, it is possible to further expand the dynamic range relatingto the direction in which the illuminance is high. Furthermore, in aconfiguration in which a color filter is arranged on each pixel Px, aneffect of suppressing color mixing can also be obtained. The voltageapplied to the third electrode 15 may be supplied from the voltagesupply circuit 150.

(Second Operation Example of Imaging Device 100A)

Next, a second example of an operation of the imaging device 100A willbe described. In the aforementioned first example, a voltage selectedfrom the first voltage range is used as the first voltage V1, and avoltage selected from the second voltage range is used as the secondvoltage V2. However, there is no restriction to this example, and boththe first voltage V1 and the second voltage V2 may be voltages selectedfrom the second voltage range, for example.

As depicted in FIG. 4 , a change in the level of the signals withrespect to a change in the quantity of light incident on thephotoelectric conversion units 10, in the second voltage range isrelatively small compared to that in the first voltage range, and, inthe example depicted in FIG. 4 , it can be said that the photoelectricconversion units 10 indicate photoelectric conversion characteristicsthat are comparatively flat in the second voltage range. The secondvoltage range, for example, can be a voltage region in which a change inthe level of the signals with respect to a change in the quantity oflight incident on the photoelectric conversion units 10 is 25% or less.“A change in the level of the signals with respect to a change in thequantity of incident light being 25% or less” is a change thatcorresponds to ⅓ of the difference between two adjacent levels whenconverted into International Organization for Standardization-standards(ISO-standards).

By selecting specific values for the first voltage V1 and the secondvoltage V2 from the voltages within the second voltage range,photographing at a sensitivity that corresponds to the illuminancebecomes possible while ensuring linearity. For example, a voltage of 6 Vcan be used as the first voltage V1, and a voltage of 12 V can be usedas the second voltage V2. In the example depicted in FIG. 4 , thephotoelectric conversion efficiency η produced when the first voltage V1is applied to the opposite electrode 11 is approximately 0.87, and thevalue of the photoelectric conversion efficiency η produced when thesecond voltage V2 is applied is approximately 1.0. The value of theratio for these η values is approximately 1.15. In a case where specificvalues for the first voltage V1 and the second voltage V2 are selectedfrom voltages within the second voltage range, the ratio of thephotoelectric conversion efficiency η produced when the second voltageV2 is applied to the opposite electrode 11 with respect to the value ofthe photoelectric conversion efficiency η produced when the firstvoltage V1 is applied to the opposite electrode 11 may be greater than 1and less than or equal to 1.25.

FIG. 17 schematically depicts a typical example of a change in the levelof the signals from the output circuits 20, with respect to a change inthe quantity of light incident on the photoelectric conversion units 10,when the first voltage V1 is applied to the opposite electrode 11, andwhen the second voltage V2 is applied to the opposite electrode 11. LineG2 in FIG. 17 depicts a change in the level of the output signals when avoltage of 6 V is applied as the first voltage V1 to the oppositeelectrode 11, and is the same as line G2 depicted in FIG. 13 . Line G3in FIG. 17 depicts a change in the level of the output signals when avoltage of 12 V is applied as the second voltage V2 to the oppositeelectrode 11. In FIG. 17 , a change in the level of the output signalswith respect to a change in the quantity of light, produced when avoltage of 2 V is applied to the opposite electrode 11, is also depictedas the dashed-line G1.

In the example of FIG. 17 , the level of the signals from the outputcircuits 20 indicates a linear change with respect to a change in thequantity of light incident on the photoelectric conversion units 10, ineither of a state in which a voltage of 6 V is applied as the firstvoltage V1 to the opposite electrode 11 and a state in which arelatively high voltage of 12 V is applied as the second voltage V2 tothe opposite electrode 11. In other words, it is understood that it ispossible to ensure linearity of the signal output with respect to achange in illuminance when either of the first voltage V1 and the secondvoltage V2 is supplied from the voltage supply circuit 150.

In the example described, the first voltage V1 is used as the voltageapplied to the voltage line 152 at the standard setting, which is commonwith the first example. Furthermore, it is possible for the operationflow in the second example to also be common with the flow describedwith reference to FIG. 8 . In other words, it is first determinedwhether or not the quantity of light incident on the photoelectricconversion units 10 is a predetermined quantity of light. In a casewhere the quantity of light incident on the photoelectric conversionunits 10 is greater than or equal to the predetermined quantity oflight, in other words, the illuminance is high, the first voltage V1 isapplied to the photoelectric conversion units 10 from the voltage supplycircuit 150. Alternatively, in a case where the quantity of lightincident on the photoelectric conversion units 10 is less than thepredetermined quantity of light, in other words, the illuminance is low,the second voltage V2 is applied to the photoelectric conversion units10 from the voltage supply circuit 150.

FIG. 18 is a schematic cross-sectional view for describing an operationof the pixels Px at a high illuminance. In a case where the quantity oflight incident on the photoelectric conversion units 10 is greater thanor equal to the predetermined quantity of light, the first voltage V1 isapplied to the opposite electrode 11. Here, a voltage of 6 V, which isapproximately an intermediate magnitude, is applied to the oppositeelectrode 11. As already described, due to exposure, there is anincrease in the electron holes accumulated in the impurity region 111serving as a charge accumulation unit, and therefore the potential ofthe impurity region 111 gradually rises. Consequently, the effectivebias voltage according to the photoelectric conversion layer 13 is lessthan the value of the first voltage V1, and can become approximately 5V, for example. To paraphrase this, the potential of the impurity region111 does not exceed the voltage of 6 V that is basically used as thefirst voltage V1. Therefore, high-voltage elements and element isolationregions are not required, and high reliability can be ensured.

FIG. 19 is a schematic cross-sectional view for describing an operationof the pixels Px at a low illuminance. In a case where the quantity oflight incident on the photoelectric conversion units 10 is less than thepredetermined quantity of light, the relatively high second voltage V2is applied to the opposite electrode 11. Here, a voltage of 12 V isapplied to the opposite electrode 11. As is apparent with reference toFIG. 4 , the value of the photoelectric conversion efficiency η at suchtime is higher than when the first voltage V1 is applied to the oppositeelectrode 11. In other words, the sensitivity of the pixels Px becomeshigher than when the first voltage V1 is applied to the oppositeelectrode 11, which is consequently suitable for photographing at a lowilluminance. A state in which the relatively high second voltage V2 isbeing supplied from the voltage supply circuit 150, from among the firstvoltage V1 and the second voltage V2 within the second voltage range,may be referred to as a high sensitivity mode.

As mentioned above, the potential of the impurity region 111 graduallyrises due to exposure, and the effective bias voltage according to thephotoelectric conversion layer 13 becomes less than the value of thesecond voltage V2. Consequently, the effective bias voltage according tothe photoelectric conversion layer 13 can become approximately 11 V, forexample. Similar to when the illuminance is high, in this case also, thepotential of the impurity region 111 basically does not exceed thesecond voltage V2. In other words, it is possible to suppress anincrease of the electric field applied to the impurity region 111, whilealso having a comparatively large value for the potential difference ΔVbetween the opposite electrode 11 and the pixel electrode 12.Furthermore, since the illuminance is low, the rise in the potential ofthe impurity region 111 that accompanies the accumulation of charges isalso comparatively small, and a high breakdown voltage is not requiredat portions such as the P-N junction formed between the impurity region111 and regions outside thereof or the gate insulation layer 22 g of thesignal detection transistor 22. Reliability is therefore easily ensured.

In this second example, the relatively low first voltage V1 is appliedto the voltage line 152 at the standard setting, and it is thereforepossible to suppress power consumption in ordinary photographing. Itshould be noted that using the relatively low first voltage V1 at thestandard setting is not only power efficient but is also advantageousfor increasing operation speed compared to using the second voltage V2at the standard setting. This point will be described hereinafter.

Japanese Patent No. 6202512, for example, discloses a technique forrealizing a global shutter with pixel sensitivity being substantially 0by bringing a potential difference applied between an opposite electrodeand a pixel electrode arranged on either side of a photoelectricconversion layer near to 0 V. In a case where this kind of technique isapplied, the time required for switching voltages becomes longer whenthere is a large difference between the voltage applied to the oppositeelectrode during exposure and the voltage applied to the oppositeelectrode when pixel sensitivity is set to 0 for a state to be enteredin which the shutter is electronically closed. In contrast, when thereis a small difference between voltages applied to the opposite electrodeduring exposure and during shutter use, the time required for switchingvoltages becomes shorter, and it becomes possible to execute a shutteroperation at a higher speed. Furthermore, it is possible to shorten thetime required from the end of exposure, in other words, from the voltageapplied to the opposite electrode being decreased to approximately 0, tosignal reading, and therefore driving according to the aforementionedsecond example is particularly advantageous for applying an electricalglobal shutter. The electrical global shutter is disclosed in JapanesePatent No. 6,202,512, issued Sep. 27, 2017, and U.S. Pat. No. 9,986,182,issued May 29, 2018, which are incorporated by reference herein in itsentirety.

MODIFIED EXAMPLES

FIG. 20A is a drawing depicting an exemplary circuit configuration of animaging device according to a modified example of the first embodiment.Compared to the configuration of the imaging device 100A described withreference to FIG. 1 , an imaging device 100B depicted in FIG. 20A has adetection circuit 130B instead of the detection circuit 130A. Thedetection circuit 130B does not have the comparator 134.

The detection circuit 130B, for example, includes an analog-digitalconversion circuit, and outputs digital data expressing the magnitudesof the voltages of the output signal lines S_(j) detected, to thecontrol circuit 160. The control circuit 160 determines whether or notthe level of a signal that is output from the output circuit 20 of eachpixel Px is greater than or equal to a predetermined level, on the basisof input from the detection circuit 130B. A threshold value constitutinga basis for the determination can be stored in advance in the memory162, for example. In a case where, for example, a digital value receivedfrom the detection circuit 130B is greater than or equal to thethreshold value retained in the memory 162, the control circuit 160determines that the quantity of light incident on the photoelectricconversion units 10 is greater than or equal to the predeterminedquantity of light, and causes the voltage supply circuit 150 to bedriven in such a way that the relatively low first voltage V1 is appliedto the voltage line 152. According to such a configuration it ispossible to reduce the area taken up by the detection circuit 130B onthe semiconductor substrate 110 compared to the case where thecomparator 134 is arranged inside the detection circuit. It should benoted that whether or not the quantity of light incident on thephotoelectric conversion units 10 is greater than or equal to thepredetermined quantity of light may be determined by the imageprocessing circuit 164.

In the aforementioned examples, the voltage applied to the oppositeelectrode 11 of the photoelectric conversion units 10 is switchedbetween the first voltage V1 and the second voltage V2 in accordancewith the illuminance. However, the subject for switching the appliedvoltage is not restricted to the opposite electrode 11, and the voltageapplied to the pixel electrode 12 may be switched between two voltages,as described hereinafter.

FIG. 20B depicts an exemplary circuit configuration of an imaging deviceaccording to another modified example of the first embodiment. The maindifference between the circuit configuration of an imaging device 100Cdepicted in FIG. 20B and the circuit configuration of the imaging device100A described with reference to FIG. 2 is that, in the imaging device100C, the voltage supply circuit 150 that supplies the first voltage V1and the second voltage V2 is coupled to the reset voltage line 36. Inother words, in this example, at least two mutually different voltagesare selectively supplied as the reset voltage V_(RST) to the resetvoltage line 36. It should be noted that a second voltage supply circuit154 is coupled to the voltage line 152 in the configuration exemplifiedin FIG. 20B. The second voltage supply circuit 154 basically supplies afixed voltage to the voltage line 152 during exposure. It should benoted that the voltage supply circuit 154 may be a separate componentthat is independent from the voltage supply circuit 150, or the voltagesupply circuits 150 and 154 may each be part of a single voltage supplycircuit.

The control circuit 160, which is not depicted in FIG. 20B, for example,determines whether or not the illuminance on the photoelectricconversion units 10 is greater than or equal to a predeterminedilluminance, on the basis of the level of the output signals detected bythe detection circuit 130A, before the start of a frame in which animage is to be acquired. In a case where, for example, the illuminanceon the photoelectric conversion units 10 is less than the predeterminedilluminance, the control circuit 160, for example, drives the voltagesupply circuit 150 in such a way that the relatively low first voltageV1 from among the first voltage V1 and the second voltage V2 is appliedas the reset voltage V_(RST) to the reset voltage line 36. Each pixel Pxresets the photoelectric conversion unit 10 on the basis of the firstvoltage V1, in other words, resets the potentials of the pixel electrode12 and the impurity region 111 serving as a charge accumulation unit.

Here, the voltage supply circuit 150 supplies a voltage of 1 V, forexample, as the first voltage V1 to the reset voltage line 36.Consequently, the potential of the pixel electrode 12 of each pixel Pxafter execution of the reset is 1 V. At such time, the voltage supplycircuit 154 applies a voltage of 6 V, for example, to the oppositeelectrode 11 of each pixel Px via the voltage line 152. In other words,the potential difference ΔV between the opposite electrode 11 and thepixel electrode 12 at such time is 5 V.

However, in a case where the illuminance on the photoelectric conversionunits 10 is greater than or equal to the predetermined illuminance, thatis, in an environment having a high illuminance, the relatively highsecond voltage V2 is supplied to the reset voltage line 36 from thevoltage supply circuit 150. For example, in a case where a voltage of 4V, for example, is used as the second voltage V2, the potentialdifference ΔV between the opposite electrode 11 and the pixel electrode12 decreases to 2 V compared to a state in which the first voltage V1 isapplied to the reset voltage line 36. In other words, photographing at alower sensitivity becomes possible.

In this example also, it is not essential for a voltage in the firstvoltage range to be used as the first voltage V1 and for a voltage inthe second voltage range to be used as the second voltage V2. Similar tothe aforementioned second example, voltages in the second voltage rangemay be used as both the first voltage V1 and the second voltage V2.

Here, an example has been described in which the first voltage V1 isapplied to the reset voltage line 36 in a case where the illuminance onthe photoelectric conversion units 10 is less than the predeterminedilluminance, and the relatively high second voltage V2 is applied to thereset voltage line 36 in a case where the illuminance is greater than orequal to the predetermined illuminance. However, it should be noted thatthe relationship of the applied voltage to the illuminance is notrestricted to this example. The voltage supply circuit 150 may be drivenin such a way that the second voltage V2 is applied to the reset voltageline 36 in a case where the illuminance on the photoelectric conversionunits 10 is less than the predetermined illuminance, and the relativelylow first voltage V1 is applied to the reset voltage line 36 in a casewhere the illuminance is greater than or equal to the predeterminedilluminance. At such time, a voltage that is higher than the secondvoltage V2 may be supplied to the opposite electrode 11.

Second Embodiment

FIG. 21A schematically depicts an exemplary configuration of a camerasystem according to a second embodiment of the present disclosure. Acamera system 200D depicted in FIG. 21A schematically includes animaging device 100D and a voltage supply circuit 150D.

Compared to the imaging device 100A depicted in FIG. 1 , the imagingdevice 100D depicted in FIG. 21A has a common point in including theplurality of pixels Px each having the photoelectric conversion unit 10and the output circuit 20, and the detection circuit 130A coupled to theoutput circuit 20 of each pixel Px. In the configuration exemplified inFIG. 21A, the output circuits 20 and the detection circuit 130A are bothformed on the semiconductor substrate 110. The photoelectric conversionunits 10, the output circuits 20, and the detection circuit 130A may beprovided in the form of a package in which these are integrated.

In the configuration exemplified in 21A, the voltage supply circuit 150Dis arranged within the camera system 200D in the form of a chip or apackage, for example, as an element that is separate from a package thatincludes the photoelectric conversion units 10, the output circuits 20,and the detection circuit 130A, for example. For example, the voltagesupply circuit 150D may be formed on a substrate that is different fromthe semiconductor substrate 110 on which the pixels Px are arranged.However, the voltage supply circuit 150D being coupled to one of theopposite electrode 11 and the pixel electrode 12 of each pixel Px issimilar to the first embodiment.

The operation in the camera system 200D may be similar to the firstembodiment. For example, the detection circuit 130A detects the level ofa signal that is output from the output circuit 20 of each pixel Px. Thevoltage supply circuit 150D applies the first voltage V1 to the voltageline 152 in a case where the level of the output signals detected by thedetection circuit 130A is greater than or equal to a predeterminedvoltage level, on the basis of a drive signal from the control circuit160. In a case where the level of the output signals detected by thedetection circuit 130A is lower than the predetermined voltage level,the second voltage V2 that is higher than the first voltage V1 isapplied to the voltage line 152.

In this way, it is not essential for all of the semiconductor substrate110 on which the plurality of pixels Px are formed, the row scanningcircuit 120, the detection circuit 130A, the voltage supply circuit150D, and the control circuit 160 to be integrated in the form of a chipor a package, for example. Some of these elements may be arranged inanother package or substrate, and functions similar to those of theimaging device according to the first embodiment can be demonstratedalso according to this kind of camera system configuration.

FIG. 21B schematically depicts another exemplary configuration of thecamera system according to the second embodiment of the presentdisclosure. The main difference between the camera system 200D depictedin FIG. 21A and a camera system 200E depicted in FIG. 21B is that thecamera system 200E has an imaging device 100E instead of the imagingdevice 100D. Compared to the imaging device 100D, the imaging device100E has the detection circuit 130B instead of the detection circuit130A, and, in this example, the output of the detection circuit 130B isinput to the image processing circuit 164.

In the configuration exemplified in FIG. 21B, the image processingcircuit 164 receives an output signal of the detection circuit 130B, andexecutes a comparison with a predetermined threshold value on the basisof the output signal from the detection circuit 130B. In other words,the image processing circuit 164 compares the input from the detectioncircuit 130B and a threshold value stored in the memory 162, forexample, and thereby determines whether or not the quantity of lightincident on the photoelectric conversion units 10 is greater than orequal to a predetermined quantity of light. Data indicating thedetermination result is passed to the voltage supply circuit 150D, forexample.

In a case where it has been determined that the level of the signal thatis output from the output circuit 20 of each pixel Px is greater than orequal to the predetermined level, in other words, that the quantity oflight incident on the photoelectric conversion units 10 is greater thanor equal to the predetermined quantity of light, the voltage supplycircuit 150D supplies the relatively low first voltage V1 to the voltageline 152. In a case where it has been determined that the quantity oflight incident on the photoelectric conversion units 10 is less than thepredetermined quantity of light, the voltage supply circuit 150Dsupplies the second voltage V2 to the voltage line 152.

According to a configuration such as that exemplified in FIG. 21B, thevoltage supply circuit 150D and the image processing circuit 164 arearranged within the camera system 200E in the form of elements that areseparate from the imaging device 100E, for example, separate chips orseparate packages, and therefore the degree of freedom of the design forthe voltage level used and/or the voltage input timing is improved, andmore flexible control becomes possible. Consequently, an advantage canbe obtained in that it is possible to avoid the use of a higher voltageor an increase in the chip size.

FIG. 22 schematically depicts yet another exemplary configuration of thecamera system according to the second embodiment of the presentdisclosure. A camera system 200F depicted in FIG. 22 schematicallyincludes an imaging device 100F and a light quantity detector 130F.

The imaging device 100F has a common point with the imaging device 100Adepicted in FIG. 1 in including the plurality of pixels Px each havingthe photoelectric conversion unit 10 and the output circuit 20, and thevoltage supply circuit 150 coupled to the photoelectric conversion unit10 of each pixel Px. The imaging device 100F also includes the detectioncircuit 130B coupled to the output circuits 20. The detection circuit130B has a common point with the aforementioned detection circuit 130Ain detecting the level of the signal that is output from the outputcircuit 20 of each pixel Px; however, here, the detection circuit 1306does not have the function of comparing the detected level of thesignals and a predetermined threshold value, and mainly carries outfunctions of noise-suppression signal processing, analog-digitalconversion, and the like. It should be noted that, in this example,similar to the configuration exemplified in FIG. 1 , the voltage supplycircuit 150 is coupled to the voltage line 152 coupled to the oppositeelectrodes 11, and is configured in such a way that the first voltage V1or the second voltage V2 can be selectively supplied to the oppositeelectrodes 11.

The light quantity detector 130F is arranged within the camera system200F as an element that is separate from the imaging device 100Fprovided in the form of a single chip or package, for example. The lightquantity detector 130F includes in a portion thereof a photodiode PD,for example, and detects the quantity of light incident on the imagingregion formed from the plurality of pixels Px. The light quantitydetector 130F can be a publicly known illuminance sensor moduleincluding a photoelectric conversion element such as a photodiode and anilluminance sensor IC, for example.

In the configuration exemplified in FIG. 22 , the control circuit 160determines whether or not the quantity of light incident on thephotoelectric conversion units 10 arranged in the imaging region isgreater than or equal to a predetermined quantity of light on the basisof output from the light quantity detector 130F, for example. Thecontrol circuit 160, in addition, similar to the first embodiment,determines whether to cause the first voltage V1 or the second voltageV2 to be supplied to the voltage line 152 from the voltage supplycircuit 150, in accordance with the determination result as to whetheror not the quantity of light incident on the photoelectric conversionunits 10 is greater than or equal to the predetermined quantity oflight. The voltage supply circuit 150 applies the first voltage V1 tothe voltage line 152 in a case where the quantity of light incident onthe photoelectric conversion units 10 is greater than or equal to thepredetermined quantity of light, for example, on the basis of a drivesignal from the control circuit 160. In a case where the quantity oflight incident on the photoelectric conversion units 10 is less than thepredetermined quantity of light, the second voltage V2 that is higherthan the first voltage V1 is applied to the voltage line 152.

FIG. 23 depicts a modified example of the light quantity detector.Compared to the example described with reference to FIG. 22 , a camerasystem 200G depicted in FIG. 23 has a light quantity detector 130Gincluding a light quantity detection circuit 138 instead of thephotodiode PD.

In the configuration exemplified in FIG. 23 , the light quantitydetection circuit 138 includes the comparator 134, which outputs acomparison result for the voltage levels of the output signal linesS_(j) with respect to the voltage level of the reference line 132. Inother words, in this example, the light quantity detection circuit 138detects the level of output signals from the output circuits 20, andcarries out a comparison with the voltage level of the reference line132. The comparison result is returned to the control circuit 160, andthe control circuit 160 determines whether or not the quantity of lightincident on the photoelectric conversion units 10 is greater than orequal to the predetermined quantity of light, on the basis of thedetection result according to the light quantity detection circuit 138.

In this way, instead of a direct measurement of the quantity of light bymeans of an illuminance sensor module or the like, information relatingto the quantity of light incident on the photoelectric conversion units10 may be obtained by way of detecting the level of the signals that areoutput from the pixels Px. For example, some or all of the plurality ofpixels Px arranged in the imaging region may be made to function as anilluminance sensor. The acquisition of output signals from the pixels Pxby the light quantity detector 130G may be carried out using a wiredmethod or a wireless method.

FIG. 24 schematically depicts yet another exemplary configuration of thecamera system according to the second embodiment of the presentdisclosure. A camera system 200H depicted in FIG. 24 schematicallyincludes an imaging device 100H including the plurality of pixels Pxeach having the photoelectric conversion unit 10 and the output circuit20, the voltage supply circuit 150D, and the light quantity detector130F.

In this example, the voltage supply circuit 150D and the light quantitydetector 130F are provided outside of the imaging device 100H aselements that are separate from the imaging device 100H. Similar to theexample described with reference to FIG. 22 , the control circuit 160determines whether or not the quantity of light incident on thephotoelectric conversion units 10 is greater than or equal to apredetermined quantity of light, on the basis of the quantity of lightdetected by the light quantity detector 130F. The control circuit 160causes either of the first voltage V1 and the second voltage V2 to beapplied to the voltage line 152 from the voltage supply circuit 150D, inaccordance with the determination result.

The light quantity detector 130G depicted in FIG. 23 may be appliedinstead of the light quantity detector 130F. In other words, the levelof the signal that is output from the output circuit 20 of each pixel Pxmay be obtained, and which of the first voltage V1 and the secondvoltage V2 is to be output from the voltage supply circuit 150D may bedetermined based on a comparison result between the level of the signalsfrom the output circuits 20 and the predetermined threshold value.

(Processing at Timing of Voltage Switching and Stage Thereafter)

Next, a description will be given regarding correction processingcorresponding to the timing of switching the voltage applied to thevoltage line 152. As described hereinafter, a correction correspondingto the timing of switching the voltage applied to the voltage line 152may be applied to the signal level detected by the detection circuits130A and 1306. Hereinafter, a specific example of correction processingis described with the aforementioned imaging device 100A being used asan example; however, it goes without saying that it is possible forsimilar correction processing to be applied also to the imaging devices1006 and 100C and the camera systems 200D to 200H.

FIG. 25 is a drawing for describing the relationship between the timingof switching between the first voltage V1 and the second voltage V2, anda change in the level of the signals acquired by the detection circuit130A, which accompanies the switching of the voltage. In FIG. 25 , theuppermost timing chart depicts the rise of a pulse of a verticalsynchronization signal VD, the timing chart immediately therebelowdepicts the rise of a pulse of a horizontal synchronization signal HD,and the next timing chart depicts a change in a voltage VITO that isapplied to the opposite electrodes 11 from the voltage line 152.

In FIG. 25 , in the timing chart displayed second, the period from therise of a certain pulse to the rise of the next pulse corresponds to 1H,which is one horizontal scanning period. In this 1H period, signals fromthe pixels Px belonging to a one row from among the plurality of pixelsPx are read. FIG. 25 schematically represents an operation in each rowof the plurality of pixels Px by means of rectangles that extend in thehorizontal direction. The white rectangles in FIG. 25 represent periodsin which signal charges are accumulated, in other words, exposureperiods. The shaded rectangles represent periods in which the voltagelevels of the output signal lines S_(j) are read by the detectioncircuit 130A. For simplicity, here, it is assumed that there are fiverows of the plurality of pixels Px, and an operation from row 0 to row 4is schematically depicted. In FIG. 25 , R0 to R4 respectively correspondto row 0 to row 4.

In FIG. 25 , the bidirectional arrows in the lowermost sectionschematically depict frame periods. The timing for the start of eachframe is the timing of the rise of a pulse of the verticalsynchronization signal VD. In the example depicted in FIG. 25 , thevoltage supply circuit 150 switches the voltage supplied to the oppositeelectrodes 11 from the second voltage V2 to the relatively low firstvoltage V1 at a time tc that is during the j^(th) frame period. In moredetail, in the exposure period for each row in the j^(th) frame period,the voltage applied to the voltage line 152 is switched to the firstvoltage V1.

In FIG. 25 , rectangles to which hatching has been applied schematicallydepict periods in which the first voltage V1 is applied to the oppositeelectrodes 11, within an exposure period included in the j^(th) frameperiod. As is apparent from FIG. 25 , when a rolling shutter is applied,if switching between the first voltage V1 and the second voltage V2 isexecuted in the exposure period for each row, a period in which signalcharges are accumulated while the first voltage V1 is applied to theopposite electrodes 11 and a period in which signal charges areaccumulated while the second voltage V2 is applied to the oppositeelectrodes 11 can become intermixed within one frame period. Inaddition, the ratio between the length of a period in which signalcharges are accumulated while the first voltage V1 is applied to theopposite electrodes 11 and the length of a period in which signalcharges are accumulated while the second voltage V2 is applied to theopposite electrodes 11 can be different for each row of the plurality ofpixels Px.

Therefore, with an operation such as that depicted in FIG. 25 , anadvantage can be obtained in that there is no effect from switchingvoltages in frame periods other than the frame periods in which voltageswitching is executed. However, on the other hand, vertical shading canoccur in an image that is based on pixel signals acquired in a frameperiod in which voltage switching has been executed. In other words,variations in brightness can occur in each row. However, this kind ofvertical shading caused by voltage switching can be corrected by meansof processing such as that described hereinafter.

The level of the signal that is output from a pixel Px is generallyproportional to the product of the sensitivity in the pixel Px and thelength of the exposure period for that pixel Px. Here, the photoelectricconversion unit 10 in a typical embodiment of the present disclosure canhave photoelectric conversion characteristics in which the photoelectricconversion efficiency η changes due to a change in the potentialdifference ΔV between the opposite electrode 11 and the pixel electrode12, as described with reference to FIG. 4 . In other words, sensitivityin the pixels Px changes according to the voltage supplied to thevoltage line 152 from the voltage supply circuit 150. Informationrelating to the way in which the photoelectric conversion efficiency ηof each pixel Px changes due to a change in the potential difference ΔVcan be acquired in advance by means of actual measurements or the like.Consequently, first, the product of the length T1 of a period in whichsignal charges are accumulated while the first voltage V1 is applied tothe opposite electrodes 11 and the sensitivity S1 of the pixels Px inthat period is calculated. Next, the product of the length T2 of aperiod in which signal charges are accumulated while the second voltageV2 is applied to the opposite electrodes 11 and the sensitivity S2 ofthe pixels Px in that period is calculated. A correction coefficientwith which (T1*S1+T2*S2), which is the sum of the aforementioned,becomes uniform for each row is then multiplied with a digital valuerepresenting the signal level, for example. It is thereby possible tocancel the effect of voltage switching on an image. In other words, itis sufficient for a larger gain to be applied, as the periods depictedas rectangles to which hatching has been applied in FIG. 25 becomelonger.

Processing for this kind of correction may be executed by the imageprocessing circuit 164 or the control circuit 160, for example. Thecorrection coefficient may be determined according to the magnitude of(T1*S1+T2*S2), and may be stored in the memory 162 or the like inadvance.

FIG. 26 depicts another example of the timing of switching between thefirst voltage V1 and the second voltage V2. Rectangles to which thickdiagonal hatching has been applied in FIG. 26 represent periods for anelectronic shutter so to speak, in which the reset transistor 26 isswitched to on for charges from the node FD to be discharged. FIG. 26 isan example of a case where an electronic shutter is implemented in rowunits before the start of the accumulation of signal charges in thej^(th) frame period. In this example, as schematically depicted by thebidirectional arrow ex in FIG. 26 , a period from the end of theelectronic shutter to the start of signal reading corresponds to anexposure period of the j^(th) frame period.

As depicted in FIG. 26 , also in a case where switching between thefirst voltage V1 and the second voltage V2 is executed in a scanningperiod for an electronic shutter, the ratio between the length T1 of aperiod in which signal charges are accumulated while the first voltageV1 is applied to the opposite electrodes 11 and the length T2 of aperiod in which signal charges are accumulated while the second voltageV2 is applied to the opposite electrodes 11 can be different among therows of the plurality of pixels Px.

However, also in the case where this kind of operation is applied, thevalue of the photoelectric conversion efficiency η with respect to thepotential difference ΔV is already known, and the control circuit 160can acquire information relating to the timing at which switching isperformed from the second voltage V2 to the first voltage V1 and thetiming at which signals are read. Consequently, similar to the exampledescribed with reference to FIG. 25 , it is possible to apply acorrection with which (T1*S1+T2*S2) becomes uniform in each row, and itis possible to avoid the generation of vertical shading in an image.

FIG. 27 depicts yet another example of the timing of switching betweenthe first voltage V1 and the second voltage V2. FIG. 27 is an operationexample in which switching between the first voltage V1 and the secondvoltage V2 is executed during a row scanning period for reading signalsin the j^(th) frame period. The row scanning period for reading signalsin the j^(th) frame period is schematically depicted by a bidirectionalarrow rd in FIG. 27 .

In FIG. 27 , rectangles to which hatching has been applied in R4schematically depict periods in which the first voltage V1 is applied tothe opposite electrodes 11, within an exposure period included in thej^(th) frame period. Furthermore, in FIG. 27 , rectangles to whichhatching has been applied in R0 and R1 schematically depict periods inwhich the second voltage V2 is applied to the opposite electrodes 11,within an exposure period included in the (j+1)^(th) frame period. As isapparent with reference to FIG. 27 , in a case where switching betweenthe first voltage V1 and the second voltage V2 has been executed in asignal reading period in a certain frame period, sensitivity modulationbrought about by the voltage switching affects also the accumulation ofsignal charges in the next frame period. In this case also, it ispossible to avoid the generation of vertical shading in an image byapplying a correction with which (T1*S1+T2*S2) becomes uniform in eachrow to the j^(th) frame period and the (j+1)^(th) frame period.

FIG. 28 is a drawing for describing the relationship between the timingof switching between the first voltage V1 and the second voltage V2 whena global shutter implemented by controlling the potential difference ΔVis applied, and a change in the level of signals acquired by thedetection circuit 130A, which accompanies the switching of the voltage.In the example depicted in FIG. 28 , the second voltage V2 isselectively applied to the opposite electrodes 11 in a period from afterthe end of the reading of signals relating to a (j−1)^(th) frame periodto the start of the reading of signals relating to the j^(th) frameperiod. Furthermore, the first voltage V1 is selectively applied to theopposite electrodes 11 in a period from after the end of the reading ofsignals relating to the j^(th) frame period to the start of the readingof signals relating to the (j+1)^(th) frame period. In addition, thefirst voltage V1 is selectively applied to the opposite electrodes 11 ina period from after the end of the reading of signals relating to the(j+1)^(th) frame period to the start of the reading of signals relatingto a (j+2)^(th) frame period. In other periods, the potential of theopposite electrodes 11 is made to be a positive potential in thevicinity of 0 V, in such a way that the potential difference ΔV becomessubstantially 0 V.

FIG. 28 is an operation example for when an electrical global shuttersuch as that described in the aforementioned Japanese Patent No. 6202512is applied. In FIG. 28 , periods depicted by white rectangles correspondto periods for the substantial accumulation of signal charges, in otherwords, exposure periods. In this example, in the (j+1)^(th) frameperiod, although it can be said that switching from the second voltageV2 to the first voltage V1 is executed, an accumulation of signalcharges substantially does not occur in periods in which the potentialof the opposite electrodes 11 is made to be a potential in the vicinityof 0 V, and therefore there is no generation of vertical shading causedby switching the voltage applied to the opposite electrodes 11.Consequently, the aforementioned correction processing is not required.In this way, the correction processing is not required depending on theoperation mode of the imaging device. Therefore, it is not necessary forthe aforementioned correction processing to be applied in every case,and it is sufficient for the correction processing to be executed asrequired. Whether or not correction processing corresponding toswitching between the first voltage V1 and the second voltage V2 is tobe executed may be switched on the basis of the operation mode of theimaging device, a user command, or the like.

Furthermore, in a case where photographing is to be executed at a framerate that is sufficiently high, a correction with which (T1*S1+T2*S2)becomes uniform in each row can be omitted. FIG. 29 is a drawing fordescribing an example of the relationship between the timing ofswitching between the first voltage V1 and the second voltage V2, and anoutput from the imaging device 100A. In FIG. 29 , the rectangles drawnbelow the chart depicting a change in the voltage VITO schematicallydepict whether image data that is based on the signal level detected bythe detection circuit 130A is valid or invalid.

Similar to the example described with reference to FIG. 25 , in theexample depicted in FIG. 29 , switching between the first voltage V1 andthe second voltage V2 is executed in the exposure period of each row ofthe j^(th) frame period. Therefore, in a case where correctionprocessing is not carried out, vertical shading caused by voltageswitching can occur in an image that is based on pixel signals acquiredin the j^(th) frame period.

However, in a case where the frame rate is sufficiently high, even ifpixel signals acquired in frame periods in which there is a possibilityof the generation of vertical shading due to voltage switching, namelythe j^(th) frame period in this example, are discarded as invalid data,as schematically depicted in FIG. 29 , it can be said that the effectthereof is small. In this way, in a case where the frame rate issufficiently high, pixel signals acquired in frame periods in whichthere is a possibility of the generation of vertical shading may bediscarded as invalid data, and pixel signals acquired in other frameperiods may be selectively acquired as valid data. In the presentspecification, processing in which pixel signals acquired in frameperiods that has a possibility of vertical shading are discarded asinvalid data, is referred to as mask processing. This kind of maskprocessing is effective in a case where it is difficult to ensure aregion for mounting a circuit for executing corrections with which(T1*S1+T2*S2) becomes uniform in each row.

FIG. 30 depicts an application example of mask processing in a casewhere switching between the first voltage V1 and the second voltage V2has been executed during a row scanning period for reading signals. Asdescribed with reference to FIG. 27 , in a case where switching betweenthe first voltage V1 and the second voltage V2 has been executed in asignal reading period in a certain frame period, sensitivity modulationbrought about by the voltage switching affects also the accumulation ofsignal charges in the next frame period. Consequently, in a case whereswitching between the first voltage V1 and the second voltage V2 hasbeen executed during a row scanning period for reading a j^(th) signal,pixel signals acquired in j^(th) frame period and pixel signals acquiredin the (j+1)^(th) frame period may be set as targets for the maskprocessing as invalid data, as schematically depicted in FIG. 30 .

It is sufficient for the aforementioned mask processing to be executedas required, and it is beneficial for it to be possible to switchbetween whether or not the mask processing is to be executed. The maskprocessing can be executed by a logic circuit arranged in the controlcircuit 160, for example, or the image processing circuit 164. Theselection of data may be executed by an analog-digital conversioncircuit in the detection circuit 130A.

(Reflection of Detected Exposure Quantity on Potential Difference ΔV inAutomatic Exposure Setting Process)

It is not necessary for the voltages that can be supplied to theopposite electrodes 11 or the pixel electrodes 12 by the aforementionedvoltage supply circuits 150, 150D, and 154 to be restricted to the twovalues of the first voltage V1 and the second voltage V2. The voltagesupply circuits 150, 150D, and 154 may be configured so as to be able toselectively apply any voltages of three or more values to the voltageline 152 in accordance with the environment in which photographing iscarried out, for example. For example, as described hereinafter, thevoltage supply circuit 150, 150D, or 154 may be configured so as toapply a voltage to the voltage line 152 with switching being performedbetween voltages of three or more values, in accordance with theexposure quantity, that is, the illuminance on the photoelectricconversion units 10.

FIG. 31 is a drawing for describing an example of a processing sequencein an automatic exposure setting process, which can be applied in animaging device and a camera system according to the embodiments of thepresent disclosure. The graph depicted in FIG. 31 depicts examples ofchanges in the exposure quantity for each frame period.

The exposure quantity indicated by the vertical axis of FIG. 31 can becalculated as described hereinafter, for example. As schematicallydepicted in FIG. 32 , a region including the photoelectric conversionunits 10 of the plurality of pixels Px is taken as an imaging region Rm,and an arbitrary region including the photoelectric conversion units 10of one or more pixels Px from within the imaging region Rm is taken as adetection region Rd. At such time, the exposure quantity indicated bythe vertical axis of FIG. 31 can be calculated by detecting, for eachframe period, the level of the signals from the output circuits 20 ofthe pixels Px located in the detection region Rd. For example, anaverage value for the level of the signals from the output circuits 20of the pixels Px located in the detection region Rd can be made tocorrespond to the exposure quantity. Instead of detecting signal levelsby means of the detection circuit 130A or 1306, the exposure quantityfor each frame period may be estimated by means of the light quantitydetector 130F or 130G.

FIG. 33 depicts an example of processing in which a voltage that isoutput from the voltage supply circuit is altered according to theexposure quantity detected. FIG. 33 depicts a graph of changes inexposure quantity for each frame period, and a graph indicating changesin the voltage VITO applied to the opposite electrodes 11 from thevoltage line 152, together as one drawing. The graph in the uppersection of FIG. 33 is the same as the graph depicted in FIG. 31 . In theexample depicted in FIG. 33 , in a case where an exposure quantityexceeding a predetermined threshold value Ex1 is detected in a certainframe period, the voltage that is output from the voltage supply circuit150 is switched to a lower voltage.

In the example depicted in FIG. 33 , if attention is directed to thethird frame period, for example, the acquired exposure quantity exceedsthe value Ex1. Therefore, the voltage supply circuit 150 switches thevoltage supplied to the voltage line 152 from the second voltage V2 to athird voltage V3 that is lower. Consequently, in the next fourth frameperiod, signal charges are accumulated in a state in which therelatively low third voltage V3 is applied to the opposite electrodes11. In a case where the photoelectric conversion units 10 havephotoelectric conversion characteristics such as those depicted in FIG.4 , for example, the sensitivity of the pixels Px decreases togetherwith a decrease in the voltage applied to the photoelectric conversionunits 10. Over-exposure can therefore be avoided.

It should be noted that, in this example, the exposure quantity acquiredin the fourth frame period still exceeds the threshold value Ex1.Consequently, the voltage supply circuit 150 further reduces the voltagesupplied to the voltage line 152, and applies a fourth voltage V4 to thephotoelectric conversion units 10. In a case where the exposure quantityacquired in the fifth frame period still exceeds the threshold valueEx1, the voltage supply circuit 150 applies an even lower fifth voltageV5 to the voltage line 152, as depicted in FIG. 33 . In this example,the exposure quantity acquired in the sixth frame period is less than orequal to the threshold value Ex1, and therefore, in the seventh frameperiod, the voltage applied to the opposite electrodes 11 remains as thefifth voltage V5. The aforementioned first voltage V1 can be any of thethird voltage V3 to the fifth voltage V5 that are lower than the secondvoltage V2.

In this way, the voltage that is output from the voltage supply circuit150 may be switched in a multistage or continuous manner in such a waythat the exposure quantity acquired in the immediately preceding frameperiod is reflected in the photoelectric conversion efficiency in thenext frame period. In addition, in a case where an exposure quantitythat is less than a predetermined threshold value Ex2 is detected in acertain frame period, processing may be executed in which the voltagethat is output from the voltage supply circuit 150 is switched to ahigher voltage.

FIG. 34 depicts another example of processing in which the voltage thatis output from the voltage supply circuit is altered according to theexposure quantity detected. Similar to FIG. 33 , FIG. 34 also depicts agraph of changes in exposure quantity for each frame period, and a graphindicating changes in the voltage VITO applied to the oppositeelectrodes 11 from the voltage line 152, together as one drawing.

In the example depicted in FIG. 34 , in a case where an exposurequantity that is less than the predetermined threshold value Ex2 isdetected in a certain frame period, the voltage that is output from thevoltage supply circuit 150 is switched to a higher voltage. In theexample depicted in FIG. 34 , the exposure quantity acquired in thethird frame period, for example, exceeds the value Ex2. Therefore, thevoltage supply circuit 150 causes the voltage supplied to the voltageline 152 to rise from the fifth voltage V5 to the fourth voltage V4. Theexposure quantity acquired in the fourth frame period is also less thanthe threshold value Ex2, and therefore the voltage supply circuit 150changes the voltage supplied to the voltage line 152 to the higher thirdvoltage V3. In a case where the exposure quantity acquired in the fifthframe period is also less than the threshold value Ex2, the voltagesupply circuit 150 applies the even higher second voltage V2 to thevoltage line 152. In this example, the exposure quantity acquired in thesixth frame period is between the threshold value Ex2 and the thresholdvalue Ex1, and therefore, in the seventh frame period, the secondvoltage V2 is applied to the opposite electrodes 11.

By setting the second threshold value Ex2 that serves as a determinationbasis for increasing the voltage that is output from the voltage supplycircuit 150, it is possible to avoid a deterioration in image qualitycaused by an insufficient exposure quantity. The second threshold valuemay be the same as the first threshold value or may be less than orequal to the first threshold value. In the examples depicted in FIGS. 31to 34 , the voltage applied to the opposite electrodes 11 or the pixelelectrodes 12 in the next frame period is determined according to acomparison result between an exposure quantity acquired in theimmediately preceding frame period and a threshold value; however, itshould be noted that the voltage applied to the opposite electrodes 11or the pixel electrodes 12 may be determined based on two or morecomparison results.

FIG. 35 depicts yet another example of processing in which the voltagethat is output from the voltage supply circuit is altered according tothe exposure quantity detected. In FIG. 35 , in a case where theexposure quantity acquired in the immediately preceding frame periodexceeds the threshold value Ex1 twice continuously, the voltage that isoutput from the voltage supply circuit 150 is switched to a lowervoltage.

If attention is directed to the third frame period, for example, theacquired exposure quantity exceeds the threshold value Ex1. At thispoint in time, the voltage that is output from the voltage supplycircuit 150 is not switched. In this example, the exposure quantityacquired in the fourth frame period does not exceed the threshold valueEx1. Therefore, the voltage that is output from the voltage supplycircuit 150 is kept at the second voltage V2.

The exposure quantity next exceeds the threshold value Ex1 in theseventh frame period. At this point in time also, the voltage that isoutput from the voltage supply circuit 150 is not switched. In thisexample, the exposure quantities acquired in the consecutive eighth totenth frame periods all exceed the threshold value Ex1. Consequently,the voltage that is output from the voltage supply circuit 150 issequentially decreased after acquisition of the exposure quantity in theeighth frame period, after acquisition of the exposure quantity in theninth frame period, and after acquisition of the exposure quantity inthe tenth frame period.

In this way, in a case where the exposure quantity acquired in theimmediately preceding frame period exceeds the threshold value or isless than the threshold value continuously a plurality of times, thevoltage that is output from the voltage supply circuit 150 may beswitched to a lower voltage or a higher voltage. According to this kindof processing, for example, when a camera stroboscope is lit, whenphotographing is carried out with a light source that periodicallyrepeats flickering, or the like, it is possible to reduce thepossibility of an over-exposed image or an under-exposed image beingacquired.

(Correction of Linearity Corresponding to Voltage Applied toPhotoelectric Conversion Units 10)

FIG. 36 schematically depicts an example of a change in the output ofthe detection circuit 130A with respect to an increase in the exposurequantity. In FIG. 36 , a solid line L1 indicates an exemplary change inthe output of the detection circuit 130A with respect to an increase inthe exposure period, in other words, an increase in the exposurequantity, at a fixed illuminance, which is obtained in a case where avoltage in the second voltage range is applied to the oppositeelectrodes 11. A dashed line L2 indicates a change in the outputobtained in a case where a lower voltage within the second voltage rangeis applied to the opposite electrodes 11. In FIG. 36 , a dashed line L3indicates an exemplary change in the output of the detection circuit130A with respect to an increase in the exposure quantity, which isobtained in a case where a voltage in the first voltage range is appliedto the opposite electrodes 11.

As described with reference to FIG. 11 , a change in the photoelectricconversion efficiency η in the photoelectric conversion layer 13 withrespect to a change in the potential difference ΔV applied between theopposite electrode 11 and the pixel electrode 12 is sometimes notlinear. Therefore, according to the magnitude of the voltage applied tothe opposite electrodes 11 or the pixel electrodes 12, the output of thedetection circuit 130A may not increase proportionally with respect toan increase in the exposure period. A tendency such as this is likely toappear particularly if the potential difference ΔV is small. In theexample depicted in FIG. 36 , the solid line L1 corresponds to a casewhere the voltage applied to the opposite electrodes 11 or the pixelelectrodes 12 is comparatively large, and the solid line L1 is linear.The dashed lines L2 and L3 correspond to a case where the voltageapplied to the opposite electrodes 11 or the pixel electrodes 12 isrelatively small, and the deviation of the dashed lines L2 and L3 from astraight line increases as the exposure quantity increases.

Thus, a deviation from a straight line of the output of the detectioncircuit 130A with respect to an increase in the exposure period may becorrected by correcting the output from the detection circuit 130A, forexample. FIG. 37 schematically depicts an overview of linearitycompensation processing. For example, a table for converting the outputfrom the detection circuit 130A into an appropriate digital value may beprepared for each voltage value that could be output from the voltagesupply circuit 150.

In this example, three correction tables 1 to 3 corresponding tovoltages that could be output from the voltage supply circuit 150 areretained in the memory 162. For example, the control circuit 160receives an output after analog-digital conversion from the detectioncircuit 130A, and applies a correction table in accordance with thespecific value of the voltage applied to the photoelectric conversionunits 10 from the voltage supply circuit 150. A selector 165 in FIG. 37is a circuit that selects which of the correction tables 1 to 3 is to beapplied, or whether a correction table is not to be applied, inaccordance with the value of the voltage that is supplied to thephotoelectric conversion units 10 from the voltage supply circuit 150.The output after correction is passed to the image processing circuit164, and gamma processing is carried out, for example.

FIG. 38 depicts an example of a correction table. In the correctiontable depicted in FIG. 38 , digital values after linearity compensationare given for each digital value that is an output from the detectioncircuit 130A. For example, when N is input as sensor output from thedetection circuit 130A, the control circuit 160 outputs X to the imageprocessing circuit 164. It should be noted that, in a case where avoltage that does not require linearity compensation is selected as avoltage to be applied to the photoelectric conversion units 10 from thevoltage supply circuit 150, as with line L1 in FIG. 36 , the sensoroutput from the detection circuit 130A is passed to the image processingcircuit 164 without being altered.

By applying this kind of linearity compensation processing, as depictedin FIG. 36 , the characteristics indicated by line L2 can be correctedas indicated by the solid straight line A2 in FIG. 36 , and thecharacteristics indicated by the graph L3 can be corrected as indicatedby the solid straight line A3. The linearity compensation processing maybe executed by the image processing circuit 164. Instead of preparing atable for pre-gamma correction output, gamma correction may be executedusing a y value that takes deviation from a straight line intoconsideration. Alternatively, instead of converting a digital valueusing a table, linearity may be compensated by multiplying sensor outputfrom the detection circuit 130A by an appropriate coefficient.

It should be noted that deviation in linearity such as theaforementioned can be different according to the imaging device oraccording to the camera system. FIG. 39 is a drawing for describingdifferences in deviation in linearity according to the imaging device oraccording to the camera system. In FIG. 39 , a dashed line M1 indicatesan exemplary change in the output of the detection circuit 130A withrespect to an increase in the exposure quantity in relation to a certainimaging device, and a dashed line M2 indicates an exemplary change inthe output of the detection circuit 130A with respect to an increase inthe exposure quantity in relation to another imaging device. It isbeneficial if the output of the detection circuit 130A with respect toan increase in the exposure quantity matches between these imagingdevices as indicated by a straight line M12 in FIG. 39 , for example.

FIG. 40 schematically depicts an overview of linearity compensationprocessing in which differences according to the imaging device oraccording to the camera system are canceled. For example, in a casewhere there is an imaging device of sample 1 and an imaging device ofsample 2, data relating to photoelectric conversion characteristics suchas those depicted in FIG. 4 is acquired in advance for samples 1 and 2using testers or the like. In addition, corrected values for each sampleare calculated based on the acquired data, and the corrected values arestored in the memory 162 in the form of a table, for example. FIG. 40depicts an overview of linearity compensation processing in sample 1,for example. Correction tables 11 to 13 for converting the output fromthe detection circuit 130A into an appropriate digital value arewritten, for each voltage value that could be output from the voltagesupply circuit 150, in the memory 162 of the imaging device of sample 1.It should be noted that the memory 162 is typically a nonvolatilememory.

FIG. 41 depicts an example of a correction table stored in the memory162 of the imaging device of sample 1, and FIG. 42 depicts an example ofa correction table stored in the memory 162 of the imaging device ofsample 2. In a case where this kind of correction table is applied, withrespect to sensor output N from the detection circuit 130A for example,a digital value X is output from the control circuit 160 of the imagingdevice of sample 1, whereas a digital value Y is output from the controlcircuit 160 of the imaging device of sample 2. By applying this kind oflinearity compensation processing that is adapted according to theimaging device or according to the camera system, as depicted in theexample of FIG. 39 , it is possible to cancel the effect of differencesin photoelectric conversion characteristics caused by individualdifferences according to the imaging device or according to the camerasystem.

As mentioned above, corrected values that are calculated based on datarelating to photoelectric conversion characteristics can be prepared foreach voltage value that could be output from the voltage supply circuit150. However, there may also be cases where exposure is carried out withthe presumed exposure time being exceeded, or where a voltage that hadnot been presumed is included in the voltages that are output from thevoltage supply circuit 150, for example.

FIG. 43 depicts another example of a correction table stored in thememory 162, and FIG. 44 depicts the plotting of output values given inthe correction table of FIG. 43 . In FIG. 44 , the white circlesindicate plots relating to corrected values that are applied when avoltage Va is applied to the photoelectric conversion units 10 from thevoltage supply circuit 150, and the white triangles indicate plotsrelating to corrected values that are applied when a voltage Vb isapplied to the photoelectric conversion units 10 from the voltage supplycircuit 150. Furthermore, the white rectangles indicate plots relatingto corrected values that are applied when a voltage Vc is applied to thephotoelectric conversion units 10 from the voltage supply circuit 150.

In a case where, for example, the value of P13 has not been obtained inadvance in the correction table of FIG. 43 , the value of P13 can becomputed by means of linear interpolation from corrected value P11 andcorrected value P12, for example. Furthermore, in a case where, forexample, a voltage that had not been presumed is applied to the voltageline 152 from the voltage supply circuit 150, it is possible to computea straight line indicating the characteristics of the output of thedetection circuit 130A with respect to an increase in the exposurequantity, from a discrete value given in the correction table. Asexemplified in FIG. 44 , if a parameter representing a straight line Ptis calculated, for example, it is possible for a corrected value forwhen an exposure quantity between t2 and t3 a and a voltage between Vband Vc are applied to the photoelectric conversion units 10 to becalculated afterward and applied in linearity compensation.

FIG. 45 schematically depicts an overview of linearity compensationprocessing including interpolation processing. As exemplified in FIG. 45, the control circuit 160 can include in a portion thereof aninterpolation processing circuit 166 that executes this kind of linearinterpolation.

The embodiments of the present disclosure can be applied tophotodetectors, image sensors, and the like, and an imaging device or acamera system of the present disclosure can be used in digital stillcameras such as digital single-lens reflex cameras and digitalmirrorless single-lens cameras, or digital video cameras, for example.Alternatively, an imaging device or a camera system of the presentdisclosure can be used in various camera systems or sensor systemsincluding commercial cameras for broadcasting uses, medical cameras,surveillance cameras, or the like. It is also possible to acquire imagesusing infrared rays by appropriately selecting the material of thephotoelectric conversion layer. An imaging device that performs imagingusing infrared rays can be used in security cameras, cameras that areused mounted on vehicles, or the like. Vehicle-mounted cameras can beused as input for a control device, for the safe travel of a vehicle,for example. Alternatively, vehicle-mounted cameras can be used tosupport an operator, for the safe travel of a vehicle.

What is claimed is:
 1. An imaging device comprising: pixel thatincludes: a photoelectric converter that converts light into a charge; acharge accumulation region to which the charge is input; and anamplifier transistor that includes a gate electrically connected to thecharge accumulation region, the amplifier transistor being configured tooutput a signal that corresponds to a potential of the chargeaccumulation region; and a detection circuit that is configured todetect a level of the signal from the amplifier transistor, wherein asensitivity of the pixel is caused to be increased, in a case where thelevel detected by the detection circuit is less than a first thresholdvalue.
 2. The imaging device according to claim 1, wherein thesensitivity of the pixel is caused to be decreased, in a case where thelevel detected by the detection circuit is greater than or equal to asecond threshold value.
 3. The imaging device according to claim 2,further comprising: a control circuit that causes the sensitivity of thepixel to be increased, in a case where the level detected by thedetection circuit is less than a first threshold value, and that causesthe sensitivity of the pixel to be decreased, in a case where the leveldetected by the detection circuit is greater than or equal to a secondthreshold value.
 4. The imaging device according to claim 1, furthercomprising: a control circuit that causes the sensitivity of the pixelto be increased, in a case where the level detected by the detectioncircuit is less than a first threshold value.
 5. A camera systemcomprising: an imaging device that includes a pixel including: aphotoelectric converter that converts light into a charge; a chargeaccumulation region to which the charge is input; and an amplifiertransistor that includes a gate electrically connected to the chargeaccumulation region, the amplifier transistor being configured to outputa signal that corresponds to a potential of the charge accumulationregion; and a light quantity detector that detects incident light,wherein a sensitivity of the pixel is caused to be increased, in a casewhere a level detected by the light quantity detector is less than afirst threshold value.
 6. The camera system according to claim 5,wherein the sensitivity of the pixel is caused to be decreased, in acase where the level detected by the light quantity detector is greaterthan or equal to a second threshold value.
 7. The imaging deviceaccording to claim 6, further comprising: a control circuit that causesthe sensitivity of the pixel to be increased, in the case where thelevel detected by the light quantity detector is less than the firstthreshold value, and that causes the sensitivity of the pixel to bedecreased, in the case where the level detected by the light quantitydetector is greater than or equal to the second threshold value.
 8. Theimaging device according to claim 5, further comprising: a controlcircuit that causes the sensitivity of the pixel to be increased, in thecase where the level detected by the light quantity detector is lessthan the first threshold value.
 9. The camera system according to claim5, wherein the photoelectric converter includes a first electrode, asecond electrode, and a photoelectric conversion layer located betweenthe first electrode and the second electrode, and the imaging deviceincludes a voltage supply circuit that applies a bias voltage betweenthe first electrode and the second electrode to cause the sensitivity ofthe pixel to be changed.
 10. The camera system according to claim 5,wherein the light quantity detector includes an illuminance sensor. 11.The camera system according to claim 5, wherein the light quantitydetector includes a photodiode.